Ferrite sintered magnet

ABSTRACT

A sintered ferrite magnet having a basic composition represented by the general formula: A 1−x−y+a Ca x+b R y+c Fe 2n−z Co z+d O 19  (atomic ratio), wherein a, b, c and d represent the amounts of an A element, Ca, an R element and Co added in the pulverization step of an oxide magnet material, which are numerals meeting the conditions of 0.03≦x≦0.4, 0.1≦y≦0.6, 0≦z≦0.4, 4≦n≦10, x+y&lt;1, 0.03≦x+b≦0.4, 0.1≦y+c≦0.6, 0.1≦z+d≦0.4, 0.50≦[(1−x−y+a)/(1−y+a+b)]≦0.97, 1.1≦(y+c)/(z+d)≦1.8, 1.0≦(y+c)/x≦20, and 0.1≦x/(z+d)≦1.2.

FIELD OF THE INVENTION

The present invention relates to a high-performance sintered ferritemagnet having higher intrinsic coercivity Hcj and residual magnetic fluxdensity Br than those of conventional sintered ferrite magnets, which isextremely suitable for a wide range of applied magnet products, such asmotors for automobiles or electric appliances, magnet rolls for copiers,etc.

BACKGROUND OF THE INVENTION

Sintered ferrite magnets having magnetoplumbite-type (M-type) structuresare used in various applications including motors, rotors of electricgenerators, etc. Sintered ferrite magnets having higher magneticproperties are recently required for the purpose of reduction in sizeand weight of motors for automobiles and increase in efficiency ofmotors for electric appliances. Sintered ferrite magnets used in motorsfor automobiles, for instance, are required to be thin for the purposeof reduction in size and weight. That is, demand is mounting forsintered ferrite magnets having high Br, as well as such high Hcj andsquareness ratio (Hk/Hcj) that their magnetization is not reduced by ademagnetization field generated when they are made thinner.

M-type sintered ferrite magnets such as Sr ferrite or Ba ferrite, etc.have conventionally been produced by the following steps. An iron oxideand a Sr or Ba carbonate, etc. are mixed and calcined to producecalcined clinker by a ferritization reaction. The calcined clinker iscoarsely pulverized, and a predetermined amount of the resultant coarsepowder is charged into a fine pulverizer, together with SiO₂, SrCO₃,CaCO₃, etc. for controlling the sintering behavior, and further Al₂O₃ orCr₂O₃ for controlling Hcj, if necessary. Wet fine pulverization isconducted in a solvent until their average diameter becomes 0.4-1.2 μm.A slurry containing the resultant fine ferrite particles is molded underpressure while orienting the fine ferrite particles in a magnetic field.The resultant green body is dried and then sintered, and finally workedto a desired shape.

The addition of Al₂O₃ or Cr₂O₃ improves Hcj but drastically reduces Br.This phenomenon occurs because Al³⁺ or Cr³⁺ dissolved in the M phaseacts to reduce saturation magnetization σs, and suppress grain growthduring sintering.

To solve this problem, Japanese Patent 3,337,990 (corresponding to U.S.Pat. No. 6,139,766) proposes a sintered ferrite magnet comprisingferrite with a hexagonal structure as a main phase, which has acomposition represented by A_(1−x)R_(x) (Fe_(12−y)M_(y))_(z)O₁₉, whereinA is at least one element selected from the group consisting of Sr, Baand Pb, Sr being indispensable, R is at least one element selected fromthe group consisting of rare earth elements including Y, La beingindispensable, M is Co or Co and Zn, and x, y and z meet the conditionsof 0.04≦x≦0.6, 0.04≦y≦0.5, and 0.7≦z≦1.2. According to the descriptionin Example 1 of Japanese Patent 3,337,990, this sintered ferrite magnetis produced by formulating a mixture of Fe₂O₃ powder, SrCO₃ powder,Co₃O₄ powder and CoO powder with La₂O₃ powder, and further with 0.2% bymass of SiO₂ powder and 0.15% by mass of CaCO₃ powder, and thencalcining, pulverizing, and molding and sintering in a magnetic field.This production step is called “prior addition method,” because La (Relement) and Co (M element) are added before calcining. The resultantsintered ferrite magnet has high Hcj and Br (Sample Nos. 11-14).However, Sample Nos. 11-14 have as low squareness ratios Hk/Hcj as77.6-84.1%. Accordingly, to meet the above requirement of furtherthinning, magnetic properties should be improved. In addition, it shouldbe noted that an extremely small amount of CaCO₃ is added in a mixingstep before calcining in Sample Nos. 11-14.

Japanese Patent 3,262,321 (corresponding to U.S. Pat. No. 6,086,781 andU.S. Pat. No. 6,258,290) discloses a method for producing a hexagonalsintered ferrite magnet having a composition comprising 1-13 atomic % ofan A element (at least one element selected from the group consisting ofSr, Ba and Ca, Sr or Ba being indispensable), 0.05-10 atomic % of an Relement (at least one element selected from the group consisting of rareearth elements including Y, or including Bi), 0.1-5 atomic % of an Melement (Co or Co and Zn), and 80-95 atomic % of Fe, the methodcomprising adding compounds containing Co and/or the R element toparticles comprising hexagonal ferrite containing at least the A elementas a main phase, or further adding compounds containing Fe and/or the Aelement, and then molding and sintering. This method is called“post-adding method,” because the R element and the M element are addedin a pulverization step after calcining. Sintered ferrite magnetsobtained by this method, however, fail to sufficiently meet therequirement of thinning, needing further improvement in magneticproperties, as is clear from Sample Nos. 1 and 2. In addition, it shouldbe noted that an extremely small amount of CaCO₃ is added in a mixingstep before calcining in Sample Nos. 1 and 2.

Japanese Patent 3,181,559 (corresponding to U.S. Pat. No. 6,402,980)discloses a sintered ferrite magnet comprising hexagonal ferrite as amain phase, and having a composition represented by the general formula:Ca_(1−x)R_(x)(Fe_(12−y)M_(y))_(z)O₁₉, wherein R is at least one elementselected from the group consisting of rare earth elements (including Y)and Bi, La being indispensable, M is Co and/or Ni, and x, y and z meetthe conditions of 0.2≦x≦0.8, 0.2≦y≦1.0, and 0.5≦z≦1.2. This sinteredferrite magnet, however, has as low Hk/Hcj as 75.9-80.6% (see SampleNos. 21-23), failing to meet the above requirement of thinning. Also, asshown in FIGS. 15 and 16 in Japanese Patent 3,181,559, when x=0.4 ormore in the composition ofCa_(x)Sr_((0.4−x))La_(0.6)Co_(0.6)Fe_(11.4)O₁₉ (x=0, 0.2, or 0.4), themagnetic properties tend to become low. This appears to be due to thefact that the Co content is as very high as 0.6.

JP11-224812A discloses a sintered ferrite magnet having both an M-typeferrite phase and a spinel ferrite phase, the M-type ferrite phasecomprising 1-13 atomic % of an A element (at least one element selectedfrom the group consisting of Sr, Ba, Ca and Pb, Sr and/or Ca beingindispensable), 0.05-10 atomic % of an R element (at least one elementselected from the group consisting of rare earth elements (including Y)and Bi), 0.1-5 atomic % of an M element (bivalent metal element such asCo, Zn, Mg, Mn, Cu, etc.), and 80-95 atomic % of Fe. However, thissintered ferrite magnet has poor magnetic properties because of havingboth the M-type ferrite phase and the spinel ferrite phase.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide ahigh-performance sintered ferrite magnet having a high residual magneticflux density Br, and a high intrinsic coercivity Hcj that does notdecrease even if it is made thinner, and further has a high squarenessratio Hk/Hcj, if necessary.

The sintered ferrite magnet of the present invention has an M-typeferrite structure, the magnet comprising as indispensable elements an Aelement, which is Sr or Sr and Ba, an R element, which is at least oneof rare earth elements including Y, La being indispensable, Ca, Fe andCo, and being produced through the steps of pulverization of an oxidemagnet material, molding and sintering, the oxide magnet material havinga basic composition represented by the following general formula (1):A_(1−x−y)Ca_(x)R_(y)Fe_(2n−z)Co_(z)O₁₉ (atomic ratio)  (1),and the sintered ferrite magnet having a basic composition representedby the following general formula (2):A_(1−x−y+a)Ca_(x+b)R_(y+c)Fe_(2n−z)Co_(z+d)O₁₉ (atomic ratio)  (2),in the above general formulae (1) and (2), x, y, z and n representingthe amounts of Ca, the R element and Co and a molar ratio in the oxidemagnet material, and a, b, c and d representing the amounts of the Aelement, Ca, the R element and Co added to the oxide magnet material inthe pulverization step, which are numerals meeting the followingconditions:

-   -   0.03≦x≦0.4,    -   0.1≦y≦0.6,    -   0≦z≦0.4,    -   4≦n≦10,    -   x+y<1,    -   0.03≦x+b≦0.4,    -   0.1≦y+c≦0.6,    -   0.1≦z+d≦0.4,    -   0.50≦[(1−x−y+a)/(1−y+a+b)]≦0.97,    -   1.1≦(y+c)/(z+d)≦1.8,    -   1.0≦(y+c)/x≦20, and    -   0.1≦x/(z+d)≦1.2.

The oxide magnet material preferably has an M phase as a main phase,particularly the oxide magnet material is a calcined body having an Mphase as a main phase.

In one embodiment of the present invention, the sintered ferrite magnetof the present invention is produced by steps comprising calcining,pulverizing, and molding and sintering after all of the A element(amount: 1−x−y, a=0) is added in the form of a compound in a mixing stepbefore calcining (called “a method of prior-adding the A element”). Toobtain high magnetic properties stably with improved sinterability, itis preferable that the A element in the form of a compound is added inan amount of (1−x−y) in a mixing step before calcining, and then in anamount of a (>0) in the pulverization step of a calcined body. Thisadding method is called “a method of prior/post-adding the A element.”

In another embodiment of the present invention, all of Ca (amount: x,b=0) is added in the form of a compound in a mixing step beforecalcining, and then subjected to the production steps of calcining,pulverization, molding and sintering to produce the sintered ferritemagnet of the present invention (called “a method of prior-adding Ca”).To increase sinterability to obtain high magnetic properties stably, itis preferable that Ca in the form of a compound is added in an amount ofx in a mixing step before calcining, and then in an amount of b (>0) inthe pulverization step of the calcined body. This adding method iscalled “a method of prior/post-adding Ca.”

In a further embodiment of the present invention, to obtain a sinteredferrite magnet having high magnetic properties, all of the R element(amount: y, c=0) and all of Co (amount: z, 0.1≦z≦0.4, d=0) arepreferably added each in the form of a compound in a mixing step beforecalcining. This adding method is called “a method of prior-adding the Relement and Co.”

In a further embodiment of the present invention, to obtain a sinteredferrite magnet having high magnetic properties, it is preferable thatall of the R element (amount: y, c=0) and part of Co (amount: z>0) areadded each in the form of a compound in a mixing step before calcining,and that the remainder of Co (amount: d>0, 0.1≦z+d≦0.4,) is added in theform of a compound in a pulverization step after calcining. This addingmethod is called “a method of prior-adding the R element andprior/post-adding Co.”

In a further embodiment of the present invention, to obtain a sinteredferrite magnet having high magnetic properties, it is preferable thatall of the R element (amount: y, c=0) is added in the form of a compoundin a mixing step before calcining, and that all of Co (amount: d,0.1≦d≦0.4, z=0) is added in the form of a compound in a pulverizationstep after calcining. This adding method is called “a method ofprior-adding the R element and post-adding Co.”

In a further embodiment of the present invention, to obtain a sinteredferrite magnet having high magnetic properties, it is preferable thatpart of the R element (amount: y) and all of Co (amount: z, 0.1≦z≦0.4,d=0) are added each in the form of a compound in a mixing step beforecalcining, and that the remainder of the R element (amount: c) is addedin the form of a compound in a pulverization step after calcining. Thisadding method is called “a method of prior/post-adding the R element andprior-adding Co.”

In a further embodiment of the present invention, to obtain a sinteredferrite magnet having high magnetic properties, it is preferable thatpart of the R element (amount: y) and part of Co (amount: z>0) are addedeach in the form of a compound in a mixing step before calcining, andthat the remainder of the R element (amount: c) and the remainder of Co(amount: d>0, 0.1≦z+d≦0.4) are added each in the form of a compound in apulverization step after calcining. This adding method is called “amethod of prior/post-adding the R element and prior/post-adding Co.”

In a further embodiment of the present invention, to obtain a sinteredferrite magnet having high magnetic properties, it is preferable thatpart of the R element (amount: y) is added in the form of a compound ina mixing step before calcining, and that the remainder of the R element(amount: c) and all of Co (amount: d, 0.1≦d≦0.4, z=0) are added each inthe form of a compound in a pulverization step after calcining. Thisadding method is called “a method of prior/post-adding the R element andpost-adding Co.”

When a d/(z+d) ratio in the prior/post-addition of Co is 0.02 or more,preferably 0.5 or more, the sintered ferrite magnet tends to haveimproved Br and/or Hcj, though not particularly restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing one example of the magnetic properties of thesintered ferrite magnet of the present invention.

FIG. 2 is a graph showing another example of the magnetic properties ofthe sintered ferrite magnet of the present invention.

FIG. 3 is a graph showing one example of the X-ray diffraction patternsof calcined ferrite in the present invention.

FIG. 4 is a graph showing another example of the X-ray diffractionpatterns of calcined ferrite in the present invention.

FIG. 5 is a graph showing one example of half widths of a (110) plane, a(107) plane and a (114) plane in the X-ray diffraction pattern ofcalcined ferrite in the present invention.

FIG. 6 is a graph showing another example of the half widths of a (110)plane, a (107) plane and a (114) plane in the X-ray diffraction patternof calcined ferrite in the present invention.

FIG. 7 is a graph showing still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 8 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 9 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 10 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 11 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 12 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 13 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 14 is a graph showing the magnetic properties of the sinteredferrite magnet of the present invention a still further example of.

FIG. 15 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 16 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 17 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

FIG. 18 is a graph showing a still further example of the magneticproperties of the sintered ferrite magnet of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1] Composition

(A) Composition of Oxide Magnet Material

The oxide magnet material of the present invention comprises an Aelement, which is Sr or Sr and Ba, an R element, which is at least oneof rare earth elements including Y, La being indispensable, Ca and Fe asindispensable elements, having a basic composition represented by thefollowing general formula:A_(1−x−y)Ca_(x)R_(y)Fe_(2n−z)Co_(z)O₁₉ (atomic ratio),wherein x, y, z and n are numerals representing the amounts of Ca, the Relement and Co and a molar ratio, which meet the following conditions:

-   -   0.03≦x≦0.4,    -   0.1≦y≦0.6,    -   0≦z≦0.4,    -   4≦n≦10, and    -   x+y≦1.

Though not particularly restricted, the conditions of0.55≦[(1−x−y)/(1−y)]≦0.97, and 1.0≦y/x≦20 are preferably met to providethe sintered ferrite magnet with good magnetic properties. When theoxide magnet material contains Co, the conditions of 0<z≦0.4;0.1≦x/z≦1.2, and 1.01≦y/z≦1.8 are preferably met to provide the sinteredferrite magnet with good magnetic properties.

To provide the sintered ferrite magnet with good magnetic properties,the Ca content (x) in the oxide magnet material is preferably 0.03-0.4,more preferably 0.05-0.3. When x is less than 0.03, a sufficient amountof Ca is not included in the M phase, resulting in an insufficientamount of R in the M phase and thus failing to achieve an effect ofimproving magnetic properties. When x exceeds 0.4, the amount of theunreacted CaO increases, resulting in generating undesirable phases suchas α-Fe₂O₃ (hematite), etc.

To provide the sintered ferrite magnet with good magnetic properties,the R content (y) in the oxide magnet material is preferably 0.1-0.6,more preferably 0.15-0.5, particularly 0.2-0.4. When y is less than 0.1,an insufficient amount of R is included in the M phase, resulting in thegeneration of undesirable phases such as α-Fe₂O₃, etc. When y exceeds0.6, the amount of the unreacted R oxide increases, resulting in thegeneration of undesirable phases such as α-Fe₂O₃, etc. R is at least oneof rare earth elements including Y, such as La, Nd, Pr, Ce, etc., and Lais indispensable. To provide the sintered ferrite magnet with goodmagnetic properties, the percentage of La in R is preferably 40 atomic %or more, more preferably 50 atomic % or more, most preferably 70 atomic% or more, particularly La alone. This is because La is most dissolvedin the M phase among the R element.

The Co content (z) in the oxide magnet material is preferably 0-0.4,more preferably 0.1-0.3. When z exceeds 0.4, Hcj decreases dramatically.When the oxide magnet material contains Co as an indispensablecomponent, a Ca/Co ratio (x/z) in the oxide magnet material ispreferably 0.1-1.2 to provide the sintered ferrite magnet with goodmagnetic properties, though not particularly restricted. Outside thisrange, it is difficult to obtain the basic composition of the sinteredferrite magnet of the present invention. The R/Co ratio (y/z) in theoxide magnet material is preferably 1.01-1.8. Outside this range, it isdifficult to obtain the basic composition of the sintered ferrite magnetof the present invention.

The molar ratio n of the oxide magnet material is preferably 4-10, morepreferably 4.6-7, most preferably 5-6. When n is outside the range of4-10, it is difficult to provide the sintered ferrite magnet of thepresent invention with good magnetic properties.

When the oxide magnet material contains the A element, Ca and the Relement in desired amounts, the sintered ferrite magnet has goodmagnetic properties. Accordingly, it is necessary to meet the conditionof 1−x−y>0, namely, x+y≦1.

The A element is Sr or Sr and Ba. To provide the sintered ferrite magnetwith good magnetic properties, the percentage of Sr in A is preferably51 atomic % or more, more preferably 70 atomic % or more, mostpreferably Sr alone. Though not particularly restricted, an Sr/(Sr+Ca)ratio [(1−x−y)/(1−y)] in the oxide magnet material is preferably0.55-0.97, more preferably 0.60-0.95. When (1−x−y)/(1−y) is outside therange of 0.55-0.97, it is difficult to obtain the basic composition ofthe sintered ferrite magnet of the present invention.

Though not particularly restricted, an R/Ca ratio (y/x) in the oxidemagnet material is preferably 1.0-20, more preferably 1.1-10. When y/xis outside the range of 1.0-20, it is difficult to obtain the basiccomposition of the sintered ferrite magnet of the present invention.

(B) Composition of Sintered Ferrite Magnet

The sintered ferrite magnet of the present invention comprising the Aelement, the R element, Ca, Fe and Co as indispensable elements has abasic composition represented by the general formula:A_(1−x−y+a)Ca_(x+b)R_(y+c)Fe_(2n−z)Co_(z+d)O₁₉ (atomic ratio), whereina, b, c and d are numerals representing the amounts of the A element,Ca, the R element and Co added in a pulverization step, which meet thefollowing conditions, and x, y, z and n represent the contents of theindispensable elements and a molar ratio in the oxide magnet material.

-   -   0.03≦x≦0.4,    -   0.1≦y≦0.6,    -   0≦z≦0.4,    -   4≦n≦10,    -   x+y≦1,    -   0.03≦x+b≦0.4,    -   0.1≦y+c≦0.6,    -   0.1≦z+d≦0.4,    -   0.50≦[(1−x−y+a)/(1−y+a+b)]≦0.97,    -   1.1≦(y+c)/(z+d)≦1.8,    -   1.0≦(y+c)/x≦20, and    -   0.1≦x/(z+d)≦1.2.

To provide the sintered ferrite magnet of the present invention withgood magnetic properties, it is further preferable to meet theconditions of 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.5, and 0≦d≦0.4, though notparticularly restricted. Namely, in the pulverization step of thesintered ferrite magnet of the present invention, the amount a of the Aelement is preferably 0-0.2, the amount b of Ca is preferably 0-0.2, theamount c of the R element is preferably 0-0.5, and the amount d of Co ispreferably 0-0.4. The term “pulverization step” used herein means acoarse or fine pulverization step. These elements may be added inamounts exceeding the ranges, but the magnetic properties ratherdecrease to less than 410 mT of Br or less than 330 kA/m of Hcj in thatcase. Accordingly, the upper limits of a, b, c and d may be set to theamounts immediately before this phenomenon occurs.

The molar ratio n′ can be determined from the formula of the basiccomposition of the sintered ferrite magnet of the present invention bythe relation of n′=(2n+d)/[2(1+a+b+c)]. n′ is preferably 4-6, morepreferably 4.5-5.8. When n′ is less than 4, non-magnetic componentsincrease, resulting in decrease in Br. When n′ exceeds 6, undesirablephases (α-Fe₂O₃, etc.) other than the M phase are generated, resultingin drastic decrease in magnetic properties.

The Ca content (x+b) in the sintered ferrite magnet of the presentinvention is preferably 0.03-0.4, more preferably 0.05-0.3. When (x+b)is less than 0.03, the inclusion of Ca in the M phase is insufficient,resulting in insufficient inclusion of R in the M phase, thus failing toachieve an effect of improving magnetic properties. When (x+b) exceeds0.4, unreacted CaO increases, resulting in the generation of undesirablephases such as α-Fe₂O₃, etc.

The R content (y+c) in the sintered ferrite magnet of the presentinvention is preferably 0.1-0.6, more preferably 0.15-0.5, particularly0.2-0.4. When (y+c) is less than 0.1, the inclusion of R in the M phaseis insufficient, failing to achieve an effect of improving magneticproperties. When (y+c) exceeds 0.6, the unreacted R oxide increases,resulting in the generation of α-Fe₂O₃, etc.

The Co content (z+d) in the sintered ferrite magnet of the presentinvention is preferably 0.1-0.4, more preferably 0.2-0.3. When (z+d) isless than 0.1, a sufficient effect of improving magnetic propertiescannot be obtained. When it exceeds 0.4, Hcj drastically decreases.

[(1−x−y+a)/(1−y+a+b)] representing the [Sr/(Sr+Ca)] ratio in thesintered ferrite magnet of the present invention is preferably0.50-0.97, more preferably 0.60-0.95. Outside the above ranges, goodmagnetic properties cannot easily be obtained.

[(y+c)/(z+d)] representing the R/Co ratio in the sintered ferrite magnetof the present invention is preferably 1.1-1.8, more preferably 1.2-1.6.Outside the above ranges, good magnetic properties cannot easily beobtained.

In the present invention, [(y+c)/x] representing the ratio of the Rcontent in the sintered ferrite magnet to the Ca content in the oxidemagnet material is preferably 1.0-20, more preferably 1.1-10. Outsidethe above ranges, good magnetic properties cannot easily be obtained.

In the present invention, [x/(z+d)] representing the ratio of the Cacontent in the oxide magnet material to the Co content in the sinteredferrite magnet is preferably 0.1-1.2, more preferably 0.2-1.1. Outsidethe above ranges, good magnetic properties cannot easily be obtained.

Though the molar number of oxygen is shown as 19 in the basiccompositions of the above oxide magnet material and sintered ferritemagnet in the present invention, this indicates a stoichiometriccomposition ratio at y=z, and n=6. However, the molar number of oxygenmay differ depending on the valences of Fe and Co, the value of n, thetype of the R element, a calcining atmosphere, and a sinteringatmosphere. Accordingly, though the molar number of oxygen is shown as19 here, it may actually be deviated from 19 to some extent.

When high Hcj is needed in the present invention, it is effective to add0.1-3.0% by mass of Cr₂O₃ or Al₂O₃ to the basic composition of the abovesintered ferrite magnet in the pulverization step, and then conductmolding and sintering. When the amount of Cr₂O₃ or Al₂O₃ added is lessthan 0.1% by mass, Hcj is not sufficiently improved. When it exceeds3.0% by mass, the Br of the sintered ferrite magnet decreasesdrastically.

[2] Production Method

(A) Production of Oxide Magnet Material

The production method of the oxide magnet material (calcined body)having the above basic composition may be a solid-phase reaction method;a liquid-phase method such as a coprecipitation method, a hydrothermalsynthesis method, etc.; a glass precipitation method; a spray thermaldecomposition method; and a vapor-phase method; which may be used aloneor in combination. Among them, the solid-phase reaction method ispractically advantageous. The oxide magnet material may be produced ascoarse powder of a single composition, or a blend of two or more typesof coarse powder, which are produced by coarsely pulverizing calcinedbodies with different calcining conditions and/or compositions, forinstance, and mixing them at arbitrary ratios, as long as it has theabove basic composition. Further, for instance, return scraps of greenbodies or sintered bodies can be used as the oxide magnet material.Taking the solid-phase reaction for example, the production method ofthe calcined ferrite will be explained in detail below.

In the solid-phase reaction method, iron oxide powder, powder containingthe A element, Ca-containing powder, powder containing the R element,and if necessary, Co-containing powder are used as starting materials,and a mixture of these powders is calcined (ferritized) to produce acalcined body (usually granules or clinker). The calcination may becarried out at 1373-1623 K, for instance, for 1 second to 10 hours,particularly about 0.1-3 hours, in the air, preferably in an atmospherehaving more than 0.05 atm of an oxygen partial pressure, particularly0.1-1.0 atm of an oxygen partial pressure. The calcined body thusobtained is substantially constituted by an M phase.

Usable compounds of the R element are, for instance, oxides, hydroxides,carbonates or organic salts of the R element. From the aspect ofindustrial production, it is preferable to use one or more of oxidessuch as La₂O₃, hydroxides such as La(OH)₃, hydrated carbonates such asLa₂(CO₃)₃.8H₂O, and organic salts such as La(CH₃CO₂)₃.1.5H₂O,La₂(C₂O₄)₃.10H₂O, etc. The use of one or more inexpensive mixed rareearth elements (La, Nd, Pr, Ce, etc.) in the form of oxides, hydroxides,carbonates or organic salts contributes to cost reduction.

Usable as Co compounds are, for instance, oxides, hydroxides orcarbonates of Co. From the aspect of industrial production, it ispreferable to use one or more of oxides such as CoO and Co₃O₄,hydroxides such as CoOOH, Co(OH)₂ and Co₃O₄.m₁H₂O (m₁ is a positivenumber), carbonates such as CoCO₃, and basic carbonates such asm₂CoCO₃.m₃Co(OH)₂.m₄H₂O (m₂, m₃ and m₄ are positive numbers).

Usable as Ca compounds are, for instance, one or more of carbonates,oxides and chlorides of Ca.

Usable as Sr compounds are, for instance, one or more of carbonates,oxides and chlorides of Sr.

(B) Pulverization of Calcined Body

The calcined body charged into a coarse pulverizer such as a vibrationmill, a roller mill, etc. is subjected to dry coarse pulverization.Taking into consideration a load received in a subsequent wet finepulverization step, etc., the coarsely pulverized powder preferably hasan average diameter of 2-5 μm. The average diameter is measured by anair permeation method using Fischer Sub-Sieve Sizer (F.S.S.S.) as ameasuring apparatus at a bulk density of 65% as a reference.

After the dry coarse pulverization, predetermined amounts of thecoarsely pulverized powder and water are charged into a wet, finepulverizer such as an attritor, a ball mill, etc., to conduct wet finepulverization. To obtain high industrial productivity and magneticproperties, the finely pulverized powder preferably has an averagediameter of 0.4-1.2 μm (measured by F.S.S.S. at a bulk density of 65% asa reference). When wet fine pulverization is conducted to obtain fineferrite particles having an average diameter of less than 0.4 μm, theHcj decreases due to abnormal crystal grain growth during sintering, anddewatering properties are low during wet molding. When the fine ferriteparticles have an average diameter exceeding 1.2 μm, the ratio of coarsecrystal grains in the sintered ferrite increases, resulting in decreasein Hcj. The average diameter of the finely pulverized powder is morepreferably 0.7-1.0 μm.

0.05-1.0% by mass of SiO₂ is preferably added to the basic compositionof the above sintered ferrite magnet at the time of wet finepulverization. The addition of SiO₂ makes it possible to obtain high Hcjstably, because the addition of SiO₂ properly suppresses the growth ofM-type ferrite particles during sintering, resulting in a dense sinteredbody. When the amount of SiO₂ added is less than 0.05%, enough addingeffect cannot be obtained. When it is more than 1.0%, there is too mucheffect of suppressing the grain growth, resulting in deterioratedsinterability and thus a drastically reduced sintering density. Theamount of SiO₂ added is more preferably 0.1-0.5%.

After the wet fine pulverization, the resultant slurry is concentratedfor use in molding. The concentration may be carried out by centrifugalseparation, filter-pressing, etc.

(C) Molding

The molding may be conducted in a dry or wet state. Molding underpressure without applying a magnetic field can produce green bodies forisotropic sintered ferrite magnets. To obtain high magnetic properties,pressure-molding in a magnetic field is preferable, thereby producinggreen bodies for anisotropic sintered ferrite magnets. To provide thegreen body with high orientation, wet molding in a magnetic field ismore preferable than dry molding in a magnetic field. In the wet-moldingstep, slurry is molded in a magnetic field. The molding pressure ispreferably about 0.1-0.5 ton/cm², and the intensity of a magnetic fieldapplied is preferably about 398-1194 kA/m.

In the case of dry molding, for instance, the slurry is dried or heatedat about 323-373 K to evaporate moisture, and then crumbled by anatomizer, etc. for use in molding. Alternatively, a green body obtainedby molding the slurry in a magnetic field is pulverized by a crasher,etc., classified by a sieve to an average diameter of about 100-700 μmto produce granules oriented in a magnetic field, which is subjected todry molding in a magnetic field. In the dry molding in a magnetic field,the pressure may be about 0.1-0.5 ton/cm², and the intensity of amagnetic field applied may be about 398-1194 kA/m.

(D) Sintering

The green body is spontaneously dried in the air or heated at 373-773 Kin the air or in a nitrogen atmosphere to remove moisture, the addeddispersant, etc. The green body is then sintered, for instance, at atemperature of preferably 1423-1573 K, more preferably 1433-1543 K inthe air or in an atmosphere having an oxygen partial pressure ofpreferably more than 0.2 atm, particularly 0.4-1.0 atm, for about 0.5-3hours. The sintered ferrite magnet of the present invention has adensity of about 4.95-5.08 g/cm³.

[3] Properties of Sintered Ferrite Magnet

The measurement of 50 M-type crystal grains by a scanning electronmicroscope in a cross section in parallel with the c-axis indicates thatthe resultant anisotropic sintered ferrite magnet has an average crystalgrain size of 3 μm or less, preferably 2 μm or less, further preferably0.5-1.0 μm, in a c-axis direction. Even if the average crystal grainsize exceeds 1.0 μm, high Hcj can be obtained in the present invention.In the present invention, anisotropy is given in the c-axis direction.

The sintered ferrite magnet of the present invention has high magneticproperties: for instance, a residual magnetic flux density Br of 410-460mT, an intrinsic coercivity Hcj of 330-478 kA/m, and a squareness ratioHk/Hcj of 85-95%, at room temperature. The Hk used herein, which is aparameter measured to obtain the Hk/Hcj, is a value on the H axis in agraph of a 4πI-H curve, wherein 4πI represents the intensity ofmagnetization and H represents the intensity of a magnetic field, at aposition in the second quadrant where 4πI is 0.95 Br. The squarenessratio is defined as a value of Hk/Hcj obtained by dividing Hk by Hcj inthe above demagnetization curve.

The sintered ferrite magnets of the present invention having excellentmagnetic properties as described above are useful for starters, powersteering and electronic throttles of automobiles, various motors, etc.They are also useful for magnet rolls for developing rolls in copiers.

The present invention will be described in detail referring to Examplesbelow without intention of restricting the scope of the presentinvention thereto.

Example 1 Investigation 1 of Amount (x) of Ca Prior-Added, with La andCo Prior-Added and Sr Prior/Post-Added

SrCO₃ powder (containing Ba and Ca as impurities), CaCO₃ powder, La(OH)₃powder (purity: 99.9%), α-Fe₂O₃ powder, and Co₃O₄ powder were mixed to abasic composition of Sr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)Co_(z)O₁₉ (n=5.7,y=0.3, z=0.26, and x=0.1, 0.2 and 0.3). 100 parts by mass of theresultant mixture was mixed with 0.2 parts by mass of SiO₂ powder. Afterwet-blending, it was dried at 423 K for 24 hours in the air, and thencalcined at 1523 K for 1 hour in the air.

The calcined body was subjected to dry coarse pulverization by a rollermill to obtain coarse powder having an average diameter of 5 μm (byF.S.S.S.). 45% by mass of coarse powder and 55% by mass of water werecharged into an attritor and subjected to wet fine pulverization to forma slurry containing fine ferrite particles having an average diameter of0.8 μm (by F.S.S.S.). In the early stage of the wet fine pulverization,0.30 parts by mass of SiO₂ powder, 0.50 parts by mass of SrCO₃ powder,and 0.80 parts by mass (0.45 parts by mass when calculated as CaO) ofCaCO₃ powder were added as sintering aids to 100 parts by mass of thecoarse powder. The resultant slurry was molded under pressure in aparallel magnetic field of 796 kA/m. The resultant green body wassintered at each temperature of 1458-1513 K for 2 hours in the air.

The resultant sintered body was Worked to a shape of 10 mm high, 10 mmwide and 20 mm thick, and measured with respect to magnetic propertiesat room temperature (20° C.) by a B-H tracer. The measurement resultsare shown in FIG. 1 (white triangle: x=0.1, white square: x=0.2, whitereverse triangle: x=0.3). The basic compositions of the calcined bodiesand the sintered bodies are shown in the rows of Sample Nos. 2-4 inTables 1 and 2.

Conventional Example 1

The same SrCO₃ powder, CaCO₃ powder, La(OH)₃ powder, α-Fe₂O₃ powder andCo₃O₄ powder as in Example 1 were mixed to a basic composition ofSr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)CO_(z)O₁₉ (n=5.7, y=0.3, z=0.26, andx=0). Subsequently, calcining, pulverizing, and molding and sintering ina magnetic field were conducted in the same manner as in Example 1, andthe resultant sintered body was measured with respect to magneticproperties at room temperature. The results are shown in FIG. 1 (whitecircle: x=0). The basic compositions of the calcined body and thesintered body are shown in the row of Sample No. 1 in Tables 1 and 2.

Comparative Example 1

The same SrCO₃ powder, CaCO₃ powder, La(OH)₃ powder, α-Fe₂O₃ powder andCo₃O₄ powder as in Example 1 were mixed to a basic composition ofSr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)Co_(z)O₁₉ (n=5.7, y=0.3, z=0.26, andx=0.4 and 0.33). Subsequently, calcining, pulverizing, and molding andsintering in a magnetic field were conducted in the same manner as inExample 1. The magnetic properties of the resultant sintered body weremeasured at room temperature. The measurement results are shown by blackcircles and black triangles in FIG. 1. The basic compositions of thecalcined bodies and the sintered bodies are shown in the rows of SampleNos. 30, 31 in Tables 1 and 2.

TABLE 1 (1 − x − y)/ No. Sample No. n x y z (1 − y) y/x x/z y/zConventional 1 5.7 0 0.3 0.26 1.0 — 0 1.15 Example 1 Example 1 2 5.7 0.10.3 0.26 0.86 3.0 0.38 1.15 3 5.7 0.2 0.3 0.26 0.71 1.5 0.77 1.15 4 5.70.3 0.3 0.26 0.57 1.0 1.15 1.15 Comparative 30 5.7 0.4 0.3 0.26 0.430.75 1.54 1.15 Example 1 31 5.7 0.33 0.3 0.26 0.53 0.91 1.27 1.15

TABLE 2 Sample (1 − x − y + a)/ (y + c)/ No. No. a b c d n′ x + b y + cz + d (1 − y + a + b) (z + d) (y + c)/x x/(z + d) Conventional 1 0.0350.082 0 0 5.10 0.082 0.30 0.26 0.90 1.15 — 0 Example 1 Example 1 2 0.0350.082 0 0 5.10 0.182 0.30 0.26 0.78 1.15 3.00 0.38 3 0.035 0.082 0 05.11 0.282 0.30 0.26 0.65 1.15 1.50 0.77 4 0.034 0.081 0 0 5.11 0.3810.30 0.26 0.53 1.15 1.00 1.15 Comparative 30 0.034 0.081 0 0 5.11 0.4810.30 0.26 0.41 1.15 0.75 1.54 Example 1 31 0.034 0.081 0 0 5.11 0.4110.30 0.26 0.49 1.15 0.91 1.27

It is clear from FIG. 1 and Tables 1 and 2 that the anisotropic sinteredferrite magnets of Example 1 having [Sr/(Sr+Ca)] ratios exceeding 49%have higher Br and Hcj than those of Conventional Example 1 andComparative Example 1.

Example 2 Investigation 2 of Amount (x) of Ca Prior-Added with La and CoPrior-Added and Sr Prior/Post-Added

Calcined bodies were produced in the same manner as in Example 1, exceptfor changing the basic compositions of calcined bodies to those ofSample Nos. 6 and 7 shown in Table 3, in which the amounts (x) of Caprior-added were 0.13 and 0.25, respectively. Subsequently, dry coarsepulverization, wet fine pulverization, and molding and sintering in amagnetic field were conducted in the same manner as in Example 1. Theresultant anisotropic sintered ferrite magnets were measured withrespect to magnetic properties at room temperature. The results areshown in FIG. 2. The basic compositions of the calcined bodies and thesintered bodies are shown in Tables 3 and 4.

Conventional Example 2

Calcining, dry coarse pulverization, wet fine pulverization, and moldingand sintering in a magnetic field were conducted in the same manner asin Example 2, except for changing the basic composition of a calcinedbody to that of Sample No. 5 shown in Table 3 (the amount (x) of Caprior-added=0). The resultant anisotropic sintered ferrite magnet wasmeasured with respect to magnetic properties at room temperature. Theresults are shown in FIG. 2. The basic compositions of the calcined bodyand the sintered body are shown in Tables 3 and 4.

Comparative Example 2

Calcining, dry coarse pulverization, wet fine pulverization, and moldingand sintering in a magnetic field were conducted in the same manner asin Example 2, except for changing the basic compositions of calcinedbodies to those of Sample Nos. 8 and 9 shown in Table 3 (the amount (x)of Ca prior-added=0.38, 0.50). The resultant anisotropic sinteredferrite magnets were measured with respect to magnetic properties atroom temperature. The results are shown in FIG. 2. The basiccompositions of the calcined body and the sintered body are shown inTables 3 and 4.

TABLE 3 Sample No. No. n x y z Conventional 5 5.42 0 0.37 0.32 Example 2Example 2 6 5.42 0.13 0.37 0.32 7 5.42 0.25 0.37 0.32 Comparative 8 5.420.38 0.37 0.32 Example 2 9 5.42 0.50 0.37 0.32 Sample (1 − x − y)/ No.No. (1 − y) y/x x/z y/z Conventional 5 1.0 — 0 1.14 Example 2 Example 26 0.79 2.85 0.39 1.14 7 0.60 1.48 0.78 1.14 Comparative 8 0.40 0.97 1.171.14 Example 2 9 0.21 0.74 1.56 1.14

TABLE 4 Sample No. No. a b c d n′ x + b y + c z + d Conven- 5 0.0340.079 0 0 4.87 0.079 0.37 0.32 tional Example 2 Example 2 6 0.033 0.0790 0 4.88 0.209 0.37 0.32 7 0.033 0.078 0 0 4.88 0.328 0.37 0.32 Compar-8 0.033 0.078 0 0 4.88 0.458 0.37 0.32 ative 9 0.033 0.077 0 0 4.880.577 0.37 0.32 Example 2 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 −y + a + b) (z + d) (y + c)/x x/(z + d) Conventional 5 0.89 1.16 — 0Example 2 Example 2 6 0.72 1.16 2.85 0.41 7 0.56 1.16 1.48 0.78Comparative 8 0.38 1.16 0.97 1.19 Example 2 9 0.22 1.16 0.74 1.56

It is clear from FIG. 2 that the anisotropic sintered ferrite magnets ofExample 2 (the amount (x) of Ca prior-added=0.13, 0.25) had highermagnetic properties than those of Conventional Example 2 and ComparativeExample 2.

Example 3 X-ray Diffraction Patterns of Calcined Bodies and MagneticProperties of Anisotropic Sintered Ferrite Magnets when Amount (x) of CaPrior-Added Changed La and Co were Prior-Added, and Sr wasPrior/Post-Added

Calcined bodies were produced in the same manner as in Example 1, exceptfor changing their basic compositions to those of Sample Nos. 66 and 67shown in Table 5 (the amounts (x) of Ca prior-added=0.13, 0.25,respectively), and changing the calcining temperature to 1518 K and 1533K, respectively. The X-ray diffraction pattern of the calcined body at acalcining temperature of 1518 K is shown in FIG. 3, and the X-raydiffraction pattern of the calcined body at a calcining temperature of1533 K is shown in FIG. 4. The X-ray diffraction was measured by a 2θ-θscanning method on the coarse powder of each calcined body set in anX-ray diffractmeter (RINT-2500 available from Rigaku Corporation) withan X-ray source of CuKa line. In FIGS. 3 and 4, the axis of ordinatesindicates an X-ray diffraction intensity, and the axis of abscissasindicates 2θ (°). FIGS. 5 and 6 show the half widths of diffractionpeaks of a (110) plane, a (107) plane and a (114) plane of the calcinedbodies at calcining temperatures of 1518 K and 1533 K, respectively. Thehalf width is a half-height width of each diffraction peak.

Each calcined body was subjected to dry coarse pulverization, wet finepulverization, and molding and sintering in a magnetic field in the samemanner as in Example 2. The measurement of the magnetic properties ofthe resultant anisotropic sintered ferrite magnets at room temperatureindicates that the anisotropic sintered ferrite magnets of Sample Nos.66 and 67 had substantially as high Br and Hcj as those of Example 2(Sample Nos. 6 and 7). The basic compositions of the calcined bodies andthe sintered bodies are shown in the rows of Sample Nos. 66 and 67 inTables 5 and 6.

Conventional Example 3

A calcined body was produced in the same manner as in Example 3, exceptfor using the basic composition shown in the row of Sample No. 65 inTable 5 (the amount (x) of Ca prior-added=0), and subjected to X-raydiffraction measurement. The results are shown in FIGS. 3-6.

The calcined body was subsequently subjected to dry coarsepulverization, wet fine pulverization, and molding and sintering in amagnetic field in the same manner as in Example 3. The measurement ofthe magnetic properties of the resultant anisotropic sintered ferritemagnet at room temperature indicates that its Br and Hcj were lower thanthose of Example 3. The basic compositions of the calcined body and thesintered body are shown in the row of Sample No. 65 in Tables 5 and 6.

Comparative Example 3

Calcined bodies were produced in the same manner as in Example 3, exceptfor using the basic compositions of Sample Nos. 68 and 69 shown in Table5 (the amount (x) of Ca prior-added=0.38, 0.50), and subjected to X-raydiffraction measurement. The results are shown in FIGS. 3-6.

Each calcined body was subjected to dry coarse pulverization, wet finepulverization, and molding and sintering in a magnetic field in the samemanner as in Example 3. The measurement of the magnetic properties ofthe resultant anisotropic sintered ferrite magnets at room temperatureindicates that their Br and Hcj were lower than those of Example 3. Thebasic compositions of the calcined bodies and the sintered bodies areshown in the rows of Sample Nos. 68 and 69 in Tables 5 and 6.

TABLE 5 Sample (1 − x − y)/ No. No. n x y z (1 − y) y/x x/z y/zConventional 65 5.42 0 0.37 0.32 1.0 — 0 1.14 Example 3 Example 3 665.42 0.13 0.37 0.32 0.79 2.85 0.39 1.14 67 5.42 0.25 0.37 0.32 0.60 1.480.78 1.14 Comparative 68 5.42 0.38 0.37 0.32 0.40 0.97 1.17 1.14 Example3 69 5.42 0.50 0.37 0.32 0.21 0.74 1.56 1.14

TABLE 6 Sample No. No. a b c d n′ x + b y + c z + d Conven- 65 0.0340.079 0 0 4.87 0.079 0.37 0.32 tional Example 3 Example 3 66 0.033 0.0790 0 4.88 0.209 0.37 0.32 67 0.033 0.078 0 0 4.88 0.328 0.37 0.32 Compar-68 0.033 0.078 0 0 4.88 0.458 0.37 0.32 ative 69 0.033 0.077 0 0 4.880.577 0.37 0.32 Example 3 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 −y + a + b) (z + d) (y + c)/x x/(z + d) Conventional 65 0.89 1.16 — 0Example 3 Example 3 66 0.72 1.16 2.85 0.41 67 0.56 1.16 1.48 0.78Comparative 68 0.38 1.16 0.97 1.19 Example 3 69 0.22 1.16 0.74 1.56

It is clear from FIGS. 3 and 4 that any calcined body was composed onlyof an M phase. FIGS. 5 and 6 show that the half width was small in0.13≦x≦0.38, suggesting that there is a small lattice crystal strain in0.13≦x≦0.38. It was found that when the compositions of the calcinedbodies of Example 3 (0.13≦x≦0.25, [Sr/(Sr+Ca)] ratio=0.60-0.79) wereselected in addition to this condition, the resultant anisotropicsintered ferrite magnets had high Br and Hcj. Namely, it was found thatwhen no Ca or too much Ca was contained, the anisotropic sinteredferrite magnets have large lattice strain, and that outside the desired[Sr/(Sr+Ca)] ratio, the resultant sintered ferrite magnets had lowmagnetic properties.

Example 4 Investigation 1 of Amount (y) of La Prior-Added, with Ca andCo Prior-Added and Sr Prior/Post-Added

Anisotropic sintered ferrite magnets were produced in the same manner asin Example 2, except for using the basic compositions of the calcinedbodies of Sample Nos. 11-15 shown in Table 7 (y=0.30-0.46), and theirmagnetic properties at room temperature were measured. The measurementresults are shown in FIG. 7. The basic compositions of the calcinedbodies and the sintered bodies are shown in Tables 7 and 8.

Comparative Example 4

An anisotropic sintered ferrite magnet was produced in the same manneras in Example 4, except for using the basic composition of the calcinedbody of Sample No. 10 shown in Table 7 (y=0.26), and its magneticproperties at room temperature were measured. The measurement resultsare shown in FIG. 7. The basic compositions of the calcined body and thesintered body are shown in Tables 7 and 8.

TABLE 7 (1 − x − y)/ No. Sample No. n x y z (1 − y) y/x x/z y/zComparative 10 5.7 0.1 0.26 0.26 0.86 2.6 0.38 1.00 Example 4 Example 411 5.7 0.1 0.30 0.26 0.86 3.0 0.38 1.15 12 5.7 0.1 0.34 0.26 0.85 3.40.38 1.31 13 5.7 0.1 0.38 0.26 0.84 3.8 0.38 1.46 14 5.7 0.1 0.42 0.260.83 4.2 0.38 1.62 15 5.7 0.1 0.46 0.26 0.81 4.6 0.38 1.77

TABLE 8 Sample No. No. n′ a b c d x + b y + c z + d Compar- 10 5.110.035 0.082 0 0 0.182 0.26 0.26 ative Example 4 Example 4 11 5.11 0.0350.082 0 0 0.182 0.30 0.26 12 5.10 0.035 0.082 0 0 0.182 0.34 0.26 135.10 0.035 0.082 0 0 0.182 0.38 0.26 14 5.10 0.035 0.083 0 0 0.183 0.420.26 15 5.10 0.035 0.083 0 0 0.183 0.46 0.26 Sample (1 − x − y + a)/(y + c)/ No. No. (1 − y + a + b) (z + d) (y + c)/x x/(z + d) Comparative10 0.79 1.00 2.60 0.38 Example 4 Example 4 11 0.78 1.15 3.00 0.38 120.77 1.31 3.40 0.38 13 0.75 1.46 3.80 0.38 14 0.74 1.62 4.20 0.38 150.72 1.77 4.60 0.38

As is clear from FIG. 7, the anisotropic sintered ferrite magnets ofExample 4 (Sample Nos. 11-15), in which (y/z) of the calcined bodies and(y+c)/(z+d) of the sintered bodies were within range of 1.1-1.8, hadhigh magnetic properties. On the other hand, the anisotropic ferritemagnet of Sample No. 10 of Comparative Example 4, in which (y/z) of thecalcined body and (y+c)/(z+d) of the sintered body were 1.00, had lowmagnetic properties.

Example 5 Investigation 2 of Amount (y) of La Prior-Added, with Ca andCo Prior-Added and Sr Prior/Post-Added

Calcining, dry coarse pulverization, wet fine pulverization, and moldingand sintering in a magnetic field were conducted to produce anisotropicsintered ferrite magnets in the same manner as in Example 2, except forusing the basic compositions of the calcined bodies of Sample Nos. 17and 18 shown in Table 9 (the amounts (y) of La prior-added=0.37, 0.41,respectively), and their magnetic properties were measured at roomtemperature. The results are shown in FIG. 8. The basic compositions ofthe calcined bodies and the sintered bodies are shown in Tables 9 and10.

Comparative Example 5

An anisotropic sintered ferrite magnet was produced in the same manneras in Example 5, except for using the basic composition of the calcinedbody of Sample No. 16 shown in Table 9 (the amount (y) of Laprior-added=0.32), and its magnetic properties were measured at roomtemperature. The results are shown in FIG. 8. The basic compositions ofthe calcined body and the sintered body are shown in Tables 9 and 10.

TABLE 9 Sample (1 − x − y)/ No. No. n x y z (1 − y) y/x x/z y/zComparative 16 5.42 0.25 0.32 0.32 0.63 1.28 0.78 1.00 Example 5 Example5 17 5.42 0.25 0.37 0.32 0.60 1.48 0.78 1.16 18 5.42 0.25 0.41 0.32 0.581.64 0.78 1.28

TABLE 10 Sample No. No. a b c d n′ x + b y + c z + d Compar- 16 0.0330.078 0 0 4.88 0.328 0.32 0.32 ative Example 5 Example 5 17 0.033 0.0780 0 4.88 0.328 0.37 0.32 18 0.033 0.078 0 0 4.88 0.328 0.41 0.32 Sample(1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b) (z + d) (y + c)/xx/(z + d) Comparative 16 0.59 1.00 1.28 0.78 Example 5 Example 5 17 0.561.16 1.48 0.78 18 0.53 1.28 1.64 0.78

As is clear from FIG. 8 and Tables 9 and 10, the anisotropic sinteredferrite magnets of Sample Nos. 17 and 18 of Example 5, in which (y/z) ofthe calcined bodies and (y+c)/(z+d) of the sintered bodies were 1.16 and1.28, respectively, had high magnetic properties. On the other hand, theanisotropic sintered ferrite magnet of Comparative Example 5, in which(y/z) of the calcined body and (y+c)/(z+d) of the sintered body were1.00, had low magnetic properties.

Example 6 Investigation of the Amounts (x, y and z) of Ca, La and CoPrior-Added, with Sr Prior/Post-Added

Calcining, dry coarse pulverization, wet fine pulverization, and moldingand sintering in a magnetic field were conducted to produce anisotropicsintered ferrite magnets in the same manner as in Example 2, except forusing the basic compositions of the calcined bodies of Sample Nos. 19-22shown in Table 11 (the amount (x) of Ca prior-added=0.10-0.25, theamount (y) of La prior-added=0.29-0.41, and the amount (z) of Coprior-added=0.24-0.32). The measurement results of magnetic propertiesat room temperature are shown in FIG. 9. The basic compositions of thecalcined bodies and the sintered bodies are shown in Tables 11 and 12.

Conventional Example 4

Anisotropic sintered ferrite magnets were produced in the same manner asin Example 6, except for using the basic compositions of the calcinedbodies of Sample Nos. 23-25 shown in Table 11 (the amount (x) of Caprior-added=0, the amount (y) of La prior-added=0.24-0.37, and theamount (z) of Co prior-added=0.20-0.32), and their magnetic propertieswere measured at room temperature. The results are shown in FIG. 9. Thebasic compositions of the calcined bodies and the sintered bodies areshown in Tables 11 and 12.

Comparative Example 6

An anisotropic sintered ferrite magnet was produced in the same manneras in Example 6, except for using the basic compositions of the calcinedbody of Sample No. 26 shown in Table 11 (the amount (x) of Caprior-added=0.52, the amount (y) of La prior-added=0.48, the amount (z)of Co prior-added=0.40, and Sr=0), and its magnetic properties weremeasured at room temperature. The results are shown in FIG. 9. The basiccompositions of the calcined body and the sintered body are shown inTables 11 and 12.

TABLE 11 Sample (1 − x − y)/ No. No. n x y z (1 − y) y/x x/z y/z Example6 19 5.71 0.10 0.29 0.24 0.86 2.90 0.43 1.20 20 5.70 0.10 0.34 0.26 0.853.40 0.38 1.31 21 5.57 0.21 0.34 0.28 0.68 1.62 0.74 1.20 22 5.42 0.250.41 0.32 0.58 1.64 0.78 1.28 Conventional 23 5.85 0 0.24 0.20 1.0 — 01.20 Example 4 24 5.70 0 0.30 0.26 1.0 — 0 1.15 25 5.42 0 0.37 0.32 1.0— 0 1.14 Comparative 26 5.15 0.52 0.48 0.40 0 0.92 1.08 1.20 Example 6

TABLE 12 Sam- ple No. No. a b c d n′ x + b y + c z + d Example 6 190.035 0.082 0 0 5.11 0.182 0.29 0.24 20 0.035 0.082 0 0 5.10 0.182 0.340.26 21 0.034 0.080 0 0 5.00 0.290 0.34 0.28 22 0.033 0.078 0 0 4.880.328 0.41 0.32 Conventional 23 0.036 0.084 0 0 5.23 0.084 0.24 0.20Example 4 24 0.035 0.082 0 0 5.10 0.082 0.30 0.26 25 0.034 0.079 0 04.87 0.079 0.37 0.32 Comparative 26 0.031 0.074 0 0 4.66 0.594 0.48 0.40Example 6 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b) (z +d) (y + c)/x x/(z + d) Example 6 19 0.78 1.21 2.90 0.42 20 0.77 1.313.40 0.38 21 0.63 1.21 1.62 0.75 22 0.53 1.28 1.64 0.78 Conventional 230.90 1.20 — 0 Example 4 24 0.90 1.15 — 0 25 0.89 1.16 — 0 Comparative 260.05 1.20 0.92 1.30 Example 6

It is clear from FIG. 9 that when the calcined bodies containing desiredamounts of Ca, La, Co and Sr are subjected to coarse pulverization, finepulverization, and molding and sintering in a magnetic field,anisotropic sintered ferrite magnets having high magnetic properties(Sample Nos. 19-22 in Example 6) can be obtained. On the other hand, theanisotropic sintered ferrite magnets of Sample Nos. 23-25 ofConventional Example 4 obtained from calcine bodies, in which theamounts of La and Co were increased without adding Ca, through drycoarse pulverization, wet fine pulverization, and molding and sinteringin a magnetic field did not have high magnetic properties. Theanisotropic ferrite magnet of Comparative Example 6 (Sample No. 26), towhich no Sr was prior-added, also had low magnetic properties.

Example 7 Investigation 3 of amount (x) of Ca Prior-Added, with La andCo Prior-Added and Sr Prior/Post-Added

The same SrCO₃ powder, CaCO₃ powder, La(OH)₃ powder, α-Fe₂O₃ powder andCo₃O₄ powder as in Example 1 were mixed to a basic composition ofSr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)Co_(z)O₁₉ (n=5.8, x=0.05-0.15, y=0.24,and z=0.2). 0.2 parts by weight of SiO₂ powder was added to 100 parts byweight of the resultant mixture. After wet-blending the mixture, it wasdried at 423 K for 24 hours in the air, and calcined at 1523 K for 1hour in the air.

The resultant calcined body was subjected to dry coarse pulverization bya vibration disc mill to obtain coarse powder having an average diameterof 5 μm (by F.S.S.S.). This coarse powder and water were subjected towet fine pulverization in an attritor to obtain a slurry of fine ferriteparticles having an average diameter of 0.8 μm (by F.S.S.S.). 0.30 partsby weight of SiO₂ powder, 0.50 parts by weight of SrCO₃ powder, and 0.80parts by weight (0.45 parts by weight when calculated as CaO) of CaCO₃powder were added as sintering aids to 100 parts by weight of thecoarsely pulverized powder in an early stage of the wet finepulverization. The resultant slurry was molded under pressure in aparallel magnetic field of 796 kA/m. The resultant green body wassintered at 1458-1513 K for 2 hours in the air. The resultant sinteredbody was worked to a shape of 10 mm high, 10 mm wide and 20 mm thick,and measured with respect to magnetic properties at room temperature bya B-H tracer. The measurement results are shown in FIG. 10. The basiccompositions of the calcined bodies and the sintered bodies are shown inthe rows of Sample Nos. 102-104 in Tables 13 and 14.

Conventional Example 5

An anisotropic sintered ferrite magnet was produced in the same manneras in Example 7 except for changing the basic composition of thecalcined body to Sr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)Co_(z)O₁₉ (n=5.8, x=0,y=0.24, and z=0.2), and its magnetic properties were measured at roomtemperature. The results are shown in FIG. 10. The basic compositions ofthe calcined body and the sintered body are shown in the row of SampleNo. 101 in Tables 13 and 14.

TABLE 13 Sam- ple (1 − x − y)/ No. No. n x y z (1 − y) y/x x/z y/zConven- 101 5.8 0 0.24 0.2 1.0 — 0 1.2 tional Example 5 Example 7 1025.8 0.05 0.24 0.2 0.93 4.8 0.25 1.2 103 5.8 0.1 0.24 0.2 0.87 2.4 0.501.2 104 5.8 0.15 0.24 0.2 0.80 1.6 0.75 1.2

TABLE 14 Sample No. No. a b c d n′ x + b y + c z + d Conven- 101 0.0350.083 0 0 5.19 0.083 0.24 0.20 tional Example 5 Example 7 102 0.0350.083 0 0 5.19 0.133 0.24 0.20 103 0.035 0.083 0 0 5.19 0.183 0.24 0.20104 0.035 0.083 0 0 5.19 0.233 0.24 0.20 Sample (1 − x − y + a)/ (y +c)/ No. No. (1 − y + a + b) (z + d) (y + c)/x x/(z + d) Conventional 1010.91 1.20 — 0 Example 5 Example 7 102 0.85 1.20 4.80 0.25 103 0.79 1.202.40 0.50 104 0.73 1.20 1.60 0.75

It is clear from FIG. 10 that the anisotropic sintered ferrite magnetsof Example 7 (Sample Nos. 102-104) had higher magnetic properties thanthose Conventional Example 5 (Sample No. 101).

Example 8 Investigation 4 of Amount (x) of Ca Prior-Added, with La andCo Prior-Added and SR Prior/Post-Added

Anisotropic sintered ferrite magnets were produced in the same manner asin Example 7 except for changing the basic composition of the calcinedbody to Sr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)Co_(z)O₁₉ (n=5.8, x=0.05-0.15,y=0.28, and z=0.2), and their magnetic properties were measured at roomtemperature. The measurement results are shown in FIG. 11. The basiccompositions of the calcined bodies and the sintered bodies are shown inthe rows of Sample Nos. 106-108 in Tables 15 and 16.

Conventional Example 6

An anisotropic sintered ferrite magnet was produced in the same manneras in Example 8 except for changing the basic composition of thecalcined body to Sr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)Co_(z)O₁₉ (n=5.8, x=0,y=0.28 and z=0.2), and its magnetic properties were measured at roomtemperature. The measurement results are shown in FIG. 11. The basiccompositions of the calcined body and the sintered body are shown in therow of Sample No. 105 in Tables 15 and 16.

TABLE 15 Sam- (1 − x − ple y)/ No. No. n x y z (1 − y) y/x x/z y/zConventional 105 5.8 0 0.28 0.2 1.0 — 0 1.4 Example 6 Example 8 106 5.80.05 0.28 0.2 0.93 5.6 0.25 1.4 107 5.8 0.1 0.28 0.2 0.86 2.8 0.50 1.4108 5.8 0.15 0.28 0.2 0.79 1.87 0.75 1.4

TABLE 16 Sample No. No. a b c d n′ x + b y + c z + d Conven- 105 0.0350.084 0 0 5.18 0.084 0.28 0.20 tional Example 6 Example 8 106 0.0350.083 0 0 5.19 0.133 0.28 0.20 107 0.035 0.083 0 0 5.19 0.183 0.28 0.20108 0.035 0.083 0 0 5.19 0.233 0.28 0.20 Sample (1 − x − y + a)/ (y +c)/ No. No. (1 − y + a + b) (z + d) (y + c)/x x/(z + d) Conventional 1050.90 1.40 — 0 Example 6 Example 8 106 0.84 1.40 5.60 0.25 107 0.78 1.402.80 0.50 108 0.72 1.40 1.87 0.75

It is clear from FIG. 11 that the anisotropic sintered ferrite magnetsof Example 8 (Sample Nos. 106-108) had higher magnetic properties thanthose of Conventional Example 6 (Sample No. 105).

Example 9 Investigation 1 of Amount (x) of Ca Prior-Added and Amount (y)of La Prior-Added, with Co Prior-Added and Sr Prior/Post-Added

Anisotropic sintered ferrite magnets were produced in the same manner asin Example 7, except for using the basic compositions of the calcinebodies of Sample Nos. 110-112 and Sample Nos. 114-116 shown in Table 17,and their magnetic properties were measured at room temperature. Themeasurement results are shown in FIG. 12. The basic compositions of theresultant calcine bodies and the sintered bodies (Sample Nos. 110-112and Sample Nos. 114-116) are shown in Tables 17 and 18.

Conventional Example 7

Anisotropic sintered ferrite magnets were produced in the same manner asin Example 9, except for using the basic compositions of the calcinebodies of Sample Nos. 109 and 113 shown in Table 17, and their magneticproperties were measured at room temperature. The measurement resultsare shown in FIG. 12. The basic compositions of the calcined bodies andthe sintered bodies are shown in Tables 17 and 18.

TABLE 17 Sam (1 − x − ple y)/ No. No. n x y z 1 − y) y/x x/z y/z Conven-109 5.8 0 0.29 0.24 1.0 — 0 1.2 tional Example 7 Example 9 110 5.8 0.050.29 0.24 0.93 5.8 0.21 1.2 111 5.8 0.10 0.29 0.24 0.86 2.9 0.42 1.2 1125.8 0.15 0.29 0.24 0.79  1.93 0.63 1.2 Conven- 113 5.8 0 0.34 0.24 1.0 —0 1.4 tional Example 7 Example 9 114 5.8 0.05 0.34 0.24 0.92 6.8 0.211.4 115 5.8 0.10 0.34 0.24 0.85 3.4 0.42 1.4 116 5.8 0.15 0.34 0.24 0.77 2.27 0.63 1.4

TABLE 18 Sample No. No. a b c d n′ x + b y + c z + d Conven- 109 0.0350.084 0 0 5.18 0.084 0.29 0.24 tional Example 7 Example 9 110 0.0350.083 0 0 5.18 0.133 0.29 0.24 111 0.035 0.083 0 0 5.19 0.183 0.29 0.24112 0.035 0.083 0 0 5.19 0.233 0.29 0.24 Conven- 113 0.036 0.084 0 05.18 0.084 0.34 0.24 tional Example 7 Example 9 114 0.035 0.084 0 0 5.180.134 0.34 0.24 115 0.035 0.084 0 0 5.18 0.184 0.34 0.24 116 0.035 0.0830 0 5.19 0.233 0.34 0.24 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 −y + a + b) (z + d) (y + c)/x x/(z + d) Conventional 109 0.90 1.21 — 0Example 7 Example 9 110 0.84 1.21 5.80 0.21 111 0.78 1.21 2.90 0.42 1120.72 1.21 1.93 0.63 Conventional 113 0.89 1.42 — 0 Example 7 Example 9114 0.83 1.42 6.80 0.21 115 0.76 1.42 3.40 0.42 116 0.70 1.42 2.27 0.63

It is clear from FIG. 12 that the anisotropic sintered ferrite magnetsof Example 9 (Sample Nos. 110-112 and Sample Nos. 114-116) had highermagnetic properties than those of Conventional Example 7 (Sample Nos.109, 113).

Example 10 Investigation 2 of Amount (x) of Ca Prior-Added and Amount(y) of La Prior-Added, with Co Prior-Added and Sr Prior/Post-Added

Anisotropic sintered ferrite magnets were produced in the same manner asin Example 7, except for using the basic compositions of the calcinebodies of Sample Nos. 117-122 shown in Table 19, and their magneticproperties were measured at room temperature. The measurement resultsare shown in FIG. 13. The basic compositions of the calcined bodies andthe sintered bodies are shown in Tables 19 and 20.

Comparative Example 7

An anisotropic sintered ferrite magnet was produced in the same manneras in Example 10, except for using the basic composition of the calcinebody of Sample No. 40 shown in Table 19, and its magnetic propertieswere measured at room temperature. The measurement results are shown inFIG. 13. The basic compositions of the calcined body and the sinteredbody are shown in Tables 19 and 20.

TABLE 19 Sam- (1 − x − ple y)/ No. No. n x y z (1 − y) y/x x/z y/zExample 117 5.8 0.10 0.39 0.28 0.84 3.9 0.36 1.4 10 118 5.8 0.15 0.390.28 0.75 2.6 0.54 1.4 119 5.8 0.20 0.39 0.28 0.67 1.95 0.71 1.4 120 5.80.10 0.45 0.28 0.82 4.5 0.36 1.6 121 5.8 0.15 0.45 0.28 0.73 3.0 0.541.6 122 5.8 0.20 0.45 0.28 0.64 2.25 0.71 1.6 Compar- 40 5.8 0 0.45 0.281.0 — — 1.6 ative Example 7

TABLE 20 Sample No. No. a b c d n′ x + b y + c z + d Example 117 0.0360.084 0 0 5.18 0.184 0.39 0.28 10 118 0.035 0.084 0 0 5.18 0.234 0.390.28 119 0.035 0.083 0 0 5.19 0.283 0.39 0.28 120 0.036 0.084 0 0 5.180.184 0.45 0.28 121 0.036 0.084 0 0 5.18 0.234 0.45 0.28 122 0.035 0.0840 0 5.18 0.284 0.45 0.28 Compar- 40 0.036 0.084 0 0 5.18 0.084 0.45 0.28ative Example 7 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b)(z + d) (y + c)/x x/(z + d) Example 10 117 0.75 1.39 3.90 0.36 118 0.681.39 2.60 0.54 119 0.61 1.39 1.95 0.71 120 0.73 1.61 4.50 0.36 121 0.651.61 3.00 0.54 122 0.58 1.61 2.25 0.71 Comparative 40 0.87 1.61 — 0Example 7

It is clear from FIG. 13 that each anisotropic sintered ferrite magnetof Example 10 had higher magnetic properties than those of ComparativeExample 7.

Example 11 Ca, La and Co Prior/Post-Added, and Sr Prior-Added

Using the same SrCO₃ powder, CaCO₃ powder, La(OH)₃ powder, α-Fe₂O₃powder and Co₃O₄ powder as in Example 1, calcined bodies were producedin the same manner as in Example 1 except for using the basiccompositions of the calcined bodies of Sample Nos. 124-126 shown inTable 21. In a wet-mixing step before calcining, 0.2 parts by mass ofSiO₂ powder was added to 100 parts by mass of the mixture. The resultantcalcined bodies were subjected to dry coarse pulverization to an averagediameter of 5 μm (by F.S.S.S.). The coarse powder was then subjected towet fine pulverization by an attritor, to obtain a slurry of fineferrite particles having an average diameter of 0.8 μm (by F.S.S.S.). Inan early stage of the fine pulverization, 0.933 parts by mass of La(OH)₃powder, 0.4 parts by mass of Co₃O₄ powder, 0.8 parts by mass of CaCO₃powder, and 0.3 parts by mass of SiO₂ powder were added to 100 parts bymass of the coarse powder in the attritor. Each of the resultantslurries was molded and sintered in a magnetic field in the same manneras in Example 1, and each resultant anisotropic sintered ferrite magnetwas measured with respect to magnetic properties at room temperature.The results are shown in FIG. 14. The anisotropic sintered ferritemagnets of Sample No. 124 sintered at 1473 K and 1483 K in the air weremeasured with respect to magnetic properties at room temperature. Themagnetic properties and average crystal grain size in a c-axis direction(measured on 50 M-type crystal grains) are shown in Table 23. The basiccompositions of the calcined bodies and the sintered bodies are shown inTables 21 and 22.

Example 12 Ca and Sr Prior/Post-Added, and La and Co Prior-Added

A calcined body was produced in the same manner as in Example 1, exceptfor mixing the same SrCO₃ powder, CaCO₃ powder, La(OH)₃ powder, α-Fe₂O₃powder and Co₃O₄ powder as in Example 1 to the basic composition of thecalcined body of Sample No. 127 shown in Table 21. In a wet-mixing stepbefore calcining, 0.2 parts by mass of SiO₂ powder was added to 100parts by mass of the mixture. The resultant calcined body was subjectedto dry coarse pulverization to an average diameter of 5 μm (byF.S.S.S.).

The resultant coarse powder and water were charged into an attritor, andfinely wet-pulverized to obtain a slurry of fine ferrite particleshaving an average diameter of 0.8 μm (by F.S.S.S.). In an early stage ofthe fine pulverization, 0.5 parts by mass of SrCO₃ powder, 0.8 parts bymass of CaCO₃ powder, and 0.3 parts by mass of SiO₂ powder were added to100 parts by mass of the coarse powder in the attritor.

The resultant slurry was molded and sintered in a magnetic field in thesame manner as in Example 1, and the resultant anisotropic sinteredferrite magnet was measured with respect to magnetic properties at roomtemperature. The measurement results were plotted as Sample No. 127 inFIG. 14. The anisotropic sintered ferrite magnet of Sample No. 127sintered at 1473 K and 1483 K was measured with respect to magneticproperties at room temperature. The magnetic properties and averagecrystal grain size in a c-axis direction (measured on 50 M-type crystalgrains) are shown in shown in Table 23. The basic compositions of thecalcined body and the sintered body are shown in the row of Sample No.127 in Tables 21 and 22.

Conventional Example 8

An anisotropic sintered ferrite magnet was produced in the same manneras in Example 1, except for using the basic composition of the calcinedbody of Sample No. 123 shown in Table 21, and its magnetic propertieswere measured at room temperature. The measurement results are shown inFIG. 14. The basic compositions of the calcined body and the sinteredbody are shown in the row of Sample No. 123 in Tables 21 and 22.

TABLE 21 Sample (1 − x − y)/ No. No. n x y z (1 − y) y/x x/z y/z x + bConventional 123 5.8 0 0.16 0.15 1.0 — 0 1.1 0.083 Example 8 Example 11124 5.8 0.05 0.17 0.15 0.94 3.4 0.34 1.2 0.133 125 5.8 0.05 0.23 0.190.94 4.6 0.26 1.2 0.133 126 5.8 0.10 0.27 0.19 0.86 2.7 0.53 1.4 0.183Example 12 127 5.8 0.05 0.21 0.19 0.94 4.2 0.26 1.1 0.133

TABLE 22 Sample No. No. a b c d n′ y + c z + d Conventional 123 0 0.0830.051 0.052 5.14 0.211 0.202 Example 8 Example 11 124 0 0.083 0.0510.052 5.14 0.221 0.202 125 0 0.083 0.051 0.052 5.14 0.281 0.242 126 00.083 0.051 0.052 5.14 0.321 0.242 Example 12 127 0.035 0.083 0 0 5.190.210 0.190 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b)(z + d) (y + c)/x x/(z + d) Conventional 123 0.91 1.04 — 0 Example 8Example 11 124 0.85 1.09 4.42 0.25 125 0.84 1.16 5.62 0.21 126 0.77 1.333.21 0.41 Example 12 127 0.85 1.11 4.20 0.26

TABLE 23 Average Crystal Sample Sintering Br Hcj Hk/Hcj Grain No. No.Temp. (K) (mT) (kA/m) (%) Size (μm) Example 11 124 1473 431 377.8 89.60.98 1483 434 357.5 90.6 1.02 Example 12 127 1473 429 358.7 87.9 0.991483 434 343.9 88.4 1.02

It is clear from FIG. 14 and Tables 21-23 that the anisotropic sinteredferrite magnets of Example 11 (Sample Nos. 124-126) (La and Coprior/post-added) obtained by adding predetermined amounts of Ca, La andCo in a mixing step before calcining, further predetermined amounts ofCa, La and Co in a pulverization step after calcining, and then moldingand sintering in a magnetic field had higher magnetic properties thanthose of Conventional Example 8 (Sample No. 123).

It is clear from FIG. 14 and Table 23 that the anisotropic sinteredferrite magnets of Example 11 (Sample No. 124, La and Coprior/post-added) had Br not lower than and Hcj and (Hk/Hcj) higher thanthose of the anisotropic sintered ferrite magnets of Example 12 (SampleNo. 127, La and Co prior-added). It is also clear from FIG. 14 that theanisotropic sintered ferrite magnets of Example 12 (Sample No. 127) hadhigh magnetic properties than those of Conventional Example 8 (SampleNo. 123).

Example 13 Comparison Between Prior/Post-Addition of Ca andPost-Addition of Ca, with La and Co Prior-Added

Calcining, coarse pulverization, wet fine pulverization, and molding andsintering in a magnetic field were conducted to produce an anisotropicsintered ferrite magnet, in the same manner as in Example 1 except forusing the basic composition of the calcined body of Sample No. 128 shownin Table 24, and its magnetic properties were measured at roomtemperature. The measurement results are shown in FIG. 15. The basiccompositions of the calcined body and the sintered body are shown in therow of Sample No. 128 in Tables 24 and 25.

Comparative Example 8

Calcining and coarse pulverization were conducted in the same manner asin Example 1 except for using the basic compositions of the calcinedbodies of Sample Nos. 129 and 130 shown in Table 24. Predeterminedamounts of the resultant coarse powder and water were charged into anattritor and finely wet-pulverized. In an early stage of the wet finepulverization, SrCO₃ powder, CaCO₃ powder and SiO₂ powder were added inamounts (parts by mass) per 100 parts by mass of the coarse powdercharged into the attritor shown in Table 26. Incidentally, as shown inTable 26, the amount of CaCO₃ added in the wet fine pulverization ofSample Nos. 129 and 130 was larger than that of CaCO₃ added in the wetfine pulverization of Sample No. 128, such that the sintered bodies ofSample Nos. 128, 129 and 130 had substantially the same basiccomposition. Using the resultant slurry of fine ferrite particles,molding and sintering in a magnetic field were conducted in the samemanner as in Example 1. The magnetic properties of the resultantanisotropic sintered ferrite magnets were measured at room temperature.The results are shown in FIG. 15. The basic compositions of the calcinedbodies and the sintered bodies are shown in the rows of Sample Nos. 129and 130 in Tables 24 and 25.

Conventional Example 9

Calcining, coarse pulverization, wet fine pulverization, and molding andsintering in a magnetic field were conducted in the same manner as inExample 1, except for using the basic composition of the calcined bodyof Sample No. 131 shown in Table 24. Incidentally, as shown in Tables24-26, the calcined body of Sample No. 131 did not contain Ca, and theamount of CaCO₃ added in the fine pulverization was the same as that ofSample No. 128. Accordingly, the sintered body of Sample No. 131 had asmaller Ca content than those of Sample Nos. 128-130. The magneticproperties of the resultant anisotropic sintered ferrite magnet weremeasured at room temperature. The results are shown in FIG. 15. Thebasic compositions of the calcined body and the sintered body are shownin the row of Sample No. 131 in Tables 24 and 25.

TABLE 24 (1 − x − y)/ No. Sample No. n x y z (1 − y) y/x x/z y/z Example13 128 5.76 0.05 0.23 0.19 0.94 4.6 0.26 1.20 Comparative 129 5.85 00.23 0.20 1.0 — 0 1.20 Example 8 130 6.06 0 0.24 0.20 1.0 — 0 1.20Conventional 131 5.76 0 0.21 0.19 1.0 — 0 1.20 Example 9

TABLE 25 Sam- ple No. No. a b c d n′ x + b y + c z + d Example 13 1280.035 0.083 0 0 5.15 0.133 0.23 0.19 Comparative 129 0 0.135 0 0 5.150.135 0.23 0.20 Example 8 130 0.037 0.139 0 0 5.15 0.139 0.24 0.20Conventional 131 0.035 0.083 0 0 5.15 0.083 0.21 0.19 Example 9 Sample(1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b) (z + d) (y + c)/xx/(z + d) Example 13 128 0.85 1.21 4.60 0.26 Comparative 129 0.85 1.15 —0 Example 8 130 0.85 1.20 — 0 Conventional 131 0.91 1.11 — 0 Example 9

TABLE 26 Sample SrCO₃ CaCO₃ SiO₂ No. No. (% by mass) (% by mass) (% bymass) Example 13 128 0.5 0.8 0.3 Comparative 129 0 1.28 0.3 Example 8130 0.5 1.28 0.3 Conventional 131 0.5 0.8 0.3 Example 9

It is clear from FIG. 15 that the anisotropic sintered ferrite magnet ofExample 13 (Sample No. 128) produced by adding a predetermined amount ofCa in a mixing step before calcining had the highest magneticproperties. The anisotropic sintered ferrite magnets of ComparativeExample 8 (Sample Nos. 129 and 130), to which Ca was added in an amountcorresponding to that in Example 13 in a pulverization step aftercalcining, had slightly improved magnetic properties, but such magneticproperties were lower than those of Example 13 (Sample No. 128). Theanisotropic sintered ferrite magnet of Conventional Example 9 (SampleNo. 131), to which Ca was not added in a mixing step before calcining,had lower magnetic properties than those of Example 13 (Sample No. 128),and further lower magnetic properties than those of Comparative Example8 (Sample Nos. 129 and 130).

FIG. 15 does not necessarily reveal why Example 13 (Sample No. 128) hadhigher magnetic properties than those of Comparative Example 8 (SampleNos. 129 and 130), but the reason therefor may be presumably thatbecause Ca added in a mixing step before calcining (Example 13) moreenters into an M phase than Ca added in a pulverization step(Comparative Example 8), higher ratios of La and Co are included in theM phase in Example 13 than in Comparative Example 8, so that Example 13had higher magnetic properties.

Example 14 Ca, La and Co Prior-Added, and Sr Prior/Post-Added

Coarse calcined body powder (powder obtained by coarsely pulverizing thecalcined body) of Sample No. 115 of Example 9 (see Table 17) having abasic composition of Sr_(1−x−y)Ca_(x)La_(y)Fe_(2n−z)Co_(z)O₁₉ (n=5.8,x=0.10, y=0.34, and z=0.24) and water were charged into an attritor inpredetermined amounts, and finely wet-pulverized to obtain a slurry offine ferrite particles having an average diameter of 0.8 μm (byF.S.S.S.). In an early stage of the wet fine pulverization, 1.68 partsby mass of SrCO₃ powder and 0.30 parts by mass of SiO₂ powder were addedto 100 parts by mass of the coarse powder charged into an attritor.Subsequently, an anisotropic sintered ferrite magnet was produced in thesame manner as in Example 1. The magnetic properties of the resultantsintered body at room temperature are shown in Table 27. The basiccompositions of the calcined body and the sintered body are shown in therow of Sample No. 141 in Tables 28 and 29.

TABLE 27 Sample Sintering Br Hcj No. No. Temp. (K) (mT) (kA/m) Example14 141 1493 428 378.0 Conventional 113 1483 426 371.6 Example 7 Example9 115 1493 433 389.1

TABLE 28 Sam- ple (1 − x − y)/ No. No. n x y z (1 − y) y/x x/z y/z Exam-141 5.8 0.10 0.34 0.24 0.85 3.4 0.42 1.4 ple 14 Con- 113 5.8 0 0.34 0.241.0 — 0 1.4 ven- tional Exam- ple 7 Exam- 115 5.8 0.10 0.34 0.24 0.853.4 0.42 1.4 ple 9

TABLE 29 Sam- ple No. No. a b c d n′ x + b y + c z + d Example 14 1410.119 0 0 0 5.18 0.10 0.34 0.24 Conventional 113 0.036 0.084 0 0 5.180.084 0.34 0.24 Example 7 Example 9 115 0.035 0.084 0 0 5.18 0.184 0.340.24 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b) (z + d)(y + c)/x x/(z + d) Example 14 141 0.87 1.42 3.4 0.42 Conventional 1130.89 1.42 — 0 Example 7 Example 9 115 0.76 1.42 3.4 0.42

It is clear from Tables 27-29 that the anisotropic sintered ferritemagnet of Example 14 (Sample No. 141), to which Ca was prior-added, hadhigher magnetic properties than those of Conventional Example 7 (SampleNo. 113).

Example 15 La Prior-Added, and Co Prior-Added

The same SrCO₃ powder, CaCO₃ powder, La(OH)₃ powder, α-Fe₂O₃ powder andCoOOH powder as in Example 1 were wet-mixed and calcined at 1523 K for 1hour in the air, to produce a calcined body having the basic compositionof Sample No. 151 shown in Table 30. In the wet-mixing step, 0.2 partsby mass of SiO₂ powder were added to 100 parts by mass of the wetmixture. The resultant calcined body was coarsely dry-pulverized to anaverage diameter of 5 μm (by F.S.S.S.), and then finely wet-pulverizedto obtain a slurry of fine ferrite particles having an average diameterof 0.8 μm (by F.S.S.S.). In an early stage of the fine pulverization,CaCO₃ powder and SiO₂ powder in amounts of 1.10 parts by mass and 0.3parts by mass, respectively, were added to 100 parts by mass of thecoarse powder charged into an attritor. The resultant slurry was moldedand sintered in a magnetic field (at 1458-1513 K for 2 hours in theair). The magnetic properties of the resultant anisotropic sinteredferrite magnet were measured at room temperature. The results areplotted as Sample No. 151 in FIG. 16. The basic compositions of thecalcined body and the sintered body are shown in the row of Sample No.151 in Tables 30 and 31.

Example 16 La Prior-Added, and Co Prior/Post-Added

A calcined body having the basic composition of Sample No. 152 shown inTable 30 was produced and coarsely dry-pulverized in the same manner asin Example 15. Predetermined amounts of the coarse powder and water werethen charged into an attritor, and finely wet-pulverized to obtain aslurry of fine ferrite particles having an average diameter of 0.8 μm(by F.S.S.S.). In an early stage of the fine pulverization, CoOOHpowder, CaCO₃ powder and SiO₂ powder were added in amounts of 1.07 partsby mass, 1.11 parts by mass and 0.3 parts by mass, respectively, to 100parts by mass of the coarse powder charged into an attritor. Theresultant slurry was subsequently molded and sintered in a magneticfield in the same manner as in Example 15, and the magnetic propertiesof the resultant anisotropic sintered ferrite magnet were measured atroom temperature. The measurement results are plotted as Sample No. 152in FIG. 16. The basic compositions of the calcined body and the sinteredbody are shown in the row of Sample No. 152 in Tables 30 and 31.

Example 17 La Prior-Added, Co Post-Added

A calcined body having the basic composition of Sample No. 153 shown inTable 30 was produced and coarsely dry-pulverized in the same manner asin Example 15. Predetermined amounts of the coarse powder and water werethen charged into an attritor, and finely wet-pulverized to obtain aslurry of fine ferrite particles having an average diameter of 0.8 μm(by F.S.S.S.). In an early stage of the fine pulverization, CoOOHpowder, CaCO₃ powder and SiO₂ powder were added in amounts of 2.15 partsby mass, 1.12 parts by mass and 0.3 parts by mass, respectively, to 100parts by mass of the coarse powder charged into an attritor. Theresultant slurry was subsequently molded and sintered in a magneticfield in the same manner as in Example 15, and the magnetic propertiesof the resultant anisotropic sintered ferrite magnet were measured atroom temperature. The measurement results were plotted as Sample No. 153in FIG. 16. The basic compositions of the calcined body and the sinteredbody are shown in the row of Sample No. 153 in Tables 30 and 31.

Example 18 La Prior/Post-Added, and Co Prior-Added

A calcined body having the basic composition of Sample No. 154 shown inTable 30 was produced and coarsely dry-pulverized in the same manner asin Example 15. Predetermined amounts of the coarse powder and water werethen charged into an attritor, and finely wet-pulverized to obtain aslurry of fine ferrite particles having an average diameter of 0.8 μm(by F.S.S.S.). In an early stage of the fine pulverization, La(OH)₃powder, CaCO₃ powder and SiO₂ powder were added in amounts of 0.47 partsby mass, 1.08 parts by mass and 0.3 parts by mass, respectively, to 100parts by mass of the coarse powder charged into the attritor. Theresultant slurry was subsequently molded and sintered in a magneticfield in the same manner as in Example 15, and the magnetic propertiesof the resultant anisotropic sintered ferrite magnet were measured atroom temperature. The measurement results were plotted as Sample No. 154in FIG. 16. The basic compositions of the calcined body and the sinteredbody are shown in the row of Sample No. 154 in Tables 30 and 31.

Example 19 La Prior/Post-Added, and Co Post-Added

A calcined body having the basic composition of Sample No. 155 shown inTable 30 was produced and coarsely dry-pulverized in the same manner asin Example 15. Predetermined amounts of the coarse powder and water werethen charged into an attritor, and finely wet-pulverized to obtain aslurry of fine ferrite particles having an average diameter of 0.8 μm(by F.S.S.S.). In an early stage of the fine pulverization, La(OH)₃powder, CoOOH powder and SiO₂ powder were added in amounts of 0.47 partsby mass, 2.07 parts by mass and 0.3 parts by mass, respectively, to 100parts by mass of the coarse powder charged into the attritor. Theresultant slurry was subsequently molded and sintered in a magneticfield in the same manner as in Example 15, and the magnetic propertiesof the resultant anisotropic sintered ferrite magnet were measured atroom temperature. The measurement results were plotted as Sample No. 155in FIG. 16. The basic compositions of the calcined body and the sinteredbody are shown in the row of Sample No. 155 in Tables 30 and 31.

TABLE 30 Sam- ple No. No. La Co n x y z Example 15 151 Prior-AddedPrior- 5.80 0.10 0.34 0.24 Added Example 16 152 Prior-Added Prior/ 5.740.10 0.34 0.12 Post- Added Example 17 153 Prior-Added Post- 5.68 0.100.34 0 Added Example 18 154 Prior/Post- Prior- 5.95 0.10 0.31 0.24 AddedAdded Example 19 155 Prior/Post- Post- 5.95 0.10 0.31 0 Added AddedSample (1 − x − y)/ No. No. (1 − y) y/x x/z y/z Example 15 151 0.85 3.40.42 1.42 Example 16 152 0.85 3.4 0.83 2.83 Example 17 153 0.85 3.4 — —Example 18 154 0.86 3.1 0.42 1.29 Example 19 155 0.86 3.1 — —

TABLE 31 Sam- ple No. No. a b c d n′ x + b y + c z + d Example 151 00.115 0 0 5.20 0.215 0.34 0.24 15 Example 152 0 0.115 0 0.12 5.20 0.2150.34 0.24 16 Example 153 0 0.115 0 0.24 5.20 0.215 0.34 0.24 17 Example154 0 0.115 0.026 0 5.21 0.215 0.34 0.24 18 Example 155 0 0.115 0.0260.24 5.32 0.215 0.34 0.24 19 Sample (1 − x − y + a)/ (y + c)/ No. No. (1− y + a + b) (z + d) (y + c)/x x/(z + d) Example 15 151 0.72 1.42 3.40.42 Example 16 152 0.72 1.42 3.4 0.42 Example 17 153 0.72 1.42 3.4 0.42Example 18 154 0.73 1.42 3.4 0.42 Example 19 155 0.73 1.42 3.4 0.42

It is clear from FIG. 16 that the anisotropic sintered ferrite magnetsof Example 15 (La: prior-added, Co: prior-added), Example 16 (La:prior-added, Co: prior/post-added), Example 17 (La: prior-added, Co:post-added), Example 18 (La: prior/post-added, Co: prior-added), andExample 19 (La: prior/post-added, Co: post-added) had magneticproperties equal to or higher than those of Examples 9, 14 shown inTable 27, and higher magnetic properties than those of ConventionalExample 7 shown in Table 27.

Example 20 Investigation of Mixed Rare Earth (R=La, Ce, Pr, Nd) StartingMaterials

SrCO₃ powder, CaCO₃ powder, R material powder (blend of two of La oxidepowder, Ce oxide powder, Pr oxide powder and Nd oxide powder), α-Fe₂O₃powder and CoOOH powder were wet-mixed and calcined at 1523 K in theair, to produce calcined bodies having the basic compositions of SampleNos. 161-163 shown in Table 32. In the wet-mixing step, 0.2 parts bymass of SiO₂ powder were added to 100 parts by mass of the mixture.Subsequently, dry coarse pulverization, wet fine pulverization, andmolding and sintering in a magnetic field were conducted in the samemanner as in Example 1. The magnetic properties of the resultantanisotropic sintered ferrite magnets were measured at room temperature.The results are plotted as Sample Nos. 161-163 in FIG. 17. The basiccompositions of the calcined bodies and the sintered bodies are shown inthe rows of Sample Nos. 161-163 in Tables 32 and 33.

TABLE 32 Sample No. No. R n x y z Example 20 161  50% La + 50% Ce 5.80.10 0.34 0.24 162  50% La + 50% Pr 5.8 0.10 0.34 0.24 163  50% La + 50%Nd 5.8 0.10 0.34 0.24 Conventional 113 100% La 5.8 0 0.34 0.24 Example 7Example 9 115 100% La 5.8 0.10 0.34 0.24 Sample (1 − x − y)/ No. No. (1− y) y/x x/z y/z Example 20 161 0.85 3.4 0.42 1.4 162 0.85 3.4 0.42 1.4163 0.85 3.4 0.42 1.4 Conventional 113 1.0 — 0 1.4 Example 7 Example 9115 0.85 3.4 0.42 1.4

TABLE 33 Sam- ple No. No. a b c d n′ x + b y + c z + d Example 20 1610.035 0.084 0 0 5.18 0.184 0.34 0.24 162 0.035 0.084 0 0 5.18 0.184 0.340.24 163 0.035 0.084 0 0 5.18 0.184 0.34 0.24 Conventional 113 0.0360.084 0 0 5.18 0.084 0.34 0.24 Example 7 Example 9 115 0.035 0.084 0 05.18 0.184 0.34 0.24 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 − y +a + b) (z + d) (y + c)/x x/(z + d) Example 20 161 0.76 1.42 3.40 0.42162 0.76 1.42 3.40 0.42 163 0.76 1.42 3.40 0.42 Conventional 113 0.891.42 — 0 Example 7 Example 9 115 0.76 1.42 3.40 0.42

It is clear from FIG. 17 that the anisotropic sintered ferrite magnetsof Example 20 (Sample Nos. 161-163) indispensably containing La as R hadhigher magnetic properties than those of Conventional Example 7 (SampleNo. 113).

Example 21 Sintering in Oxygen

The same finely pulverized slurry as in Example 9 (Sample No. 115) wasmolded in a magnetic field. The resultant green bodies were sintered at1483 K, 1493 K, 1498 K and 1503 K, respectively, for 2 hours in anoxygen atmosphere (oxygen partial pressure: 1.0 atm). The magneticproperties of the resultant anisotropic sintered ferrite magnets weremeasured at room temperature. The results are plotted as Sample No. 171in FIG. 18. The basic compositions of the calcined body and the sinteredbody are shown in the row of Sample No. 171 in Tables 34 and 35.

TABLE 34 (1 − x − y)/ No. Sample No. n x y z (1 − y) y/x x/z y/z Example21 171 5.8 0.10 0.34 0.24 0.85 3.4 0.42 1.4 Conventional 113 5.8 0 0.340.24 1.0 — 0 1.4 Example 7 Example 9 115 5.8 0.10 0.34 0.24 0.85 3.40.42 1.4

TABLE 35 Sam- ple No. No. a b c d n′ x + b y + c z + d Example 21 1710.035 0.084 0 0 5.18 0.184 0.34 0.24 Conventional 113 0.036 0.084 0 05.18 0.084 0.34 0.24 Example 7 Example 9 115 0.035 0.084 0 0 5.18 0.1840.34 0.24 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b) (z +d) (y + c)/x x/(z + d) Example 21 171 0.76 1.42 3.40 0.42 Conventional113 0.89 1.42 — 0 Example 7 Example 9 115 0.76 1.42 3.40 0.42

It is clear from FIG. 18 that the anisotropic sintered ferrite magnet ofExample 21 (Sample No. 171) sintered in oxygen had extremely highermagnetic properties than those of Conventional Example 7 (Sample No.113).

The X-ray diffraction measurement of typical calcined bodies and typicalanisotropic sintered ferrite magnets among those of Examples 1-21indicates that any of them was composed of an M phase alone.

Example 22 Anisotropic Sintered Ferrite Magnet Produced from CalcinedBody Having M Phase as Main Phase

SrCO₃ powder, CaCO₃ powder, La hydroxide powder, α-Fe₂O₃ powder andCoOOH powder were wet-mixed and calcined at 1523 K in the air, toproduce a calcined body having the basic composition of Sample No. 181shown in Table 36. Incidentally, 0.2 parts by mass of SiO₂ powder wasadded to 100 parts by mass of the mixture in a wet-mixing step beforecalcining. In the X-ray diffraction of the resultant calcined body, adiffraction pattern of α-Fe₂O₃ was observed in addition to the M phase(main phase). Subsequently, dry coarse pulverization, wet finepulverization, and molding and sintering in a magnetic field wereconducted in the same manner as in Example 1. The magnetic properties ofthe resultant anisotropic sintered ferrite magnet were measured at roomtemperature. The results are shown in Table 38. The basic compositionsof the calcined body and the sintered body are shown in the row ofSample No. 181 in Tables 36 and 37.

TABLE 36 Sam- ple (1 − x − y)/ No. No. n x y z (1 − y) y/x x/z y/z Exam-181 6.6 0.12 0.38 0.27 0.81 3.2 0.44 1.4 ple 22 Exam- 115 5.8 0.10 0.340.24 0.85 3.4 0.42 1.4 ple 9

TABLE 37 Sam- ple No. No. a b c d n′ x + b y + c z + d Example 22 1810.175 0.094 0 0 5.20 0.214 0.38 0.27 Example 9 115 0.035 0.084 0 0 5.180.184 0.34 0.24 Sample (1 − x − y + a)/ (y + c)/ No. No. (1 − y + a + b)(z + d) (y + c)/x x/(z + d) Example 22 181 0.76 1.41 3.17 0.44 Example 9115 0.76 1.42 3.40 0.42

TABLE 38 Sample Br Hcj No. No. (mT) (kA/m) Example 22 181 431 389.1Example 9 115 433 389.9

The X-ray diffraction measurement reveals that the anisotropic sinteredferrite magnet of Example 22 had an M-type ferrite structure. Table 38indicates that the anisotropic sintered ferrite magnet of Example 22produced from a calcined body having M phase as a main phase had as highmagnetic properties as those of the anisotropic sintered ferrite magnetof Example 9.

Table 39 indicates the analyzed compositions and basic compositions ofmain anisotropic sintered ferrite magnet samples used in theexperiments. The analyzed composition of each anisotropic sinteredferrite is expressed with the total of metal elements constituting themagnet being 100 atomic %. The basic composition of each anisotropicsintered ferrite magnet is expressed by x′, y′, z′ and n′ in (Sr,Ba)_(1−x′−y′)Ca_(x′)La_(y′)Fe_(2n′−z′)Co_(z′)O₁₉. x′, y′, z′ and n′represent the amounts of Ca, La and Co and a molar ratio in eachanisotropic sintered ferrite magnet. The samples with asterisk (*)belong to Conventional Examples or Comparative Examples.

TABLE 39 Analyzed Compositions (atomic %) And Basic Compositions ofAnisotropic Sintered Ferrite Magnets Sample No. Ba Sr Ca La Fe Mn Co SiAl Cr  1* 0.07 5.76 0.65 2.38 88.00 0.42 2.06 0.61 0.04 0.00  2 0.064.98 1.45 2.38 88.01 0.42 2.06 0.61 0.04 0.00  3 0.05 4.19 2.24 2.3888.01 0.42 2.06 0.61 0.04 0.00  4 0.04 3.41 3.03 2.38 88.02 0.42 2.060.60 0.04 0.00  5* 0.07 5.49 0.66 3.03 87.03 0.41 2.66 0.62 0.03 0.00  60.06 4.42 1.73 3.04 87.03 0.41 2.66 0.61 0.03 0.00  7 0.04 3.43 2.733.04 87.04 0.41 2.66 0.61 0.03 0.00  8* 0.03 2.36 3.81 3.04 87.05 0.412.66 0.60 0.03 0.00  9* 0.02 1.38 4.80 3.04 87.06 0.41 2.66 0.60 0.040.00 10* 0.07 5.29 1.44 2.06 88.01 0.42 2.06 0.61 0.04 0.00 11 0.06 4.981.45 2.38 88.01 0.42 2.06 0.61 0.04 0.00 12 0.06 4.66 1.45 2.70 88.000.42 2.06 0.61 0.04 0.00 13 0.06 4.35 1.45 3.02 88.00 0.42 2.06 0.610.04 0.00 14 0.05 4.04 1.45 3.33 88.00 0.42 2.06 0.61 0.04 0.00 15 0.053.72 1.45 3.65 87.99 0.42 2.06 0.62 0.04 0.00 16* 0.05 3.80 2.73 2.6687.05 0.41 2.66 0.61 0.03 0.00 17 0.04 3.39 2.73 3.08 87.04 0.41 2.660.61 0.03 0.00 18 0.04 3.06 2.73 3.41 87.04 0.41 2.66 0.61 0.03 0.00 190.06 5.05 1.44 2.30 88.18 0.42 1.90 0.61 0.04 0.00 20 0.06 4.66 1.452.70 88.00 0.42 2.06 0.61 0.04 0.00 21 0.05 3.88 2.35 2.76 87.64 0.412.27 0.61 0.04 0.00 22 0.04 3.06 2.73 3.41 87.04 0.41 2.66 0.61 0.030.00 23* 0.08 6.09 0.65 1.86 88.69 0.42 1.55 0.61 0.04 0.01 24* 0.075.76 0.65 2.38 88.00 0.42 2.06 0.61 0.04 0.00 25* 0.07 5.45 0.66 3.0887.03 0.41 2.66 0.62 0.03 0.00 26* 0.00 0.27 5.18 4.18 85.83 0.41 3.490.61 0.03 0.00 30* 0.03 2.62 3.82 2.38 88.03 0.42 2.06 0.60 0.04 0.0031* 0.04 3.17 3.27 2.38 88.02 0.42 2.06 0.60 0.04 0.00 40* 0.06 4.520.66 3.52 87.99 0.42 2.19 0.62 0.04 0.00 65* 0.07 5.49 0.66 3.03 87.030.41 2.66 0.62 0.03 0.00 66 0.06 4.42 1.73 3.04 87.03 0.41 2.66 0.610.03 0.00 67 0.04 3.43 2.73 3.04 87.04 0.41 2.66 0.61 0.03 0.00 68* 0.032.36 3.81 3.04 87.05 0.41 2.66 0.60 0.03 0.00 69* 0.02 1.38 4.80 3.0487.06 0.41 2.66 0.60 0.04 0.00 Sample No. x′ y′ z′ n′  1* 0.07 0.27 0.235.10  2 0.16 0.27 0.23 5.10  3 0.25 0.27 0.23 5.11  4 0.34 0.27 0.235.11  5* 0.07 0.33 0.29 4.87  6 0.19 0.33 0.29 4.88  7 0.30 0.33 0.294.88  8* 0.41 0.33 0.29 4.88  9* 0.52 0.33 0.29 4.88 10* 0.16 0.23 0.235.10 11 0.16 0.27 0.23 5.10 12 0.16 0.30 0.23 5.10 13 0.16 0.34 0.235.10 14 0.16 0.38 0.23 5.10 15 0.16 0.41 0.23 5.10 16* 0.30 0.29 0.294.88 17 0.30 0.33 0.29 4.88 18 0.30 0.37 0.29 4.88 19 0.16 0.26 0.215.11 20 0.16 0.30 0.23 5.10 21 0.26 0.31 0.25 5.00 22 0.30 0.37 0.294.88 23* 0.08 0.21 0.18 5.23 24* 0.07 0.27 0.23 5.10 25* 0.07 0.33 0.294.87 26* 0.54 0.43 0.36 4.66 30* 0.43 0.27 0.23 5.11 31* 0.37 0.27 0.235.11 40* 0.08 0.40 0.25 5.18 65* 0.07 0.33 0.29 4.87 66 0.19 0.33 0.294.88 67 0.30 0.33 0.29 4.88 68* 0.41 0.33 0.29 4.88 69* 0.52 0.33 0.294.88 Sample No. Ba Sr Ca La Fe Mn Co Si Al Cr 101* 0.08 6.14 0.65 1.8888.63 0.42 1.56 0.61 0.04 0.00 102 0.07 5.75 1.04 1.88 88.63 0.42 1.560.61 0.04 0.00 103 0.07 5.36 1.43 1.88 88.63 0.42 1.56 0.61 0.04 0.01104 0.06 4.98 1.82 1.88 88.63 0.42 1.56 0.61 0.04 0.01 105* 0.07 5.830.65 2.19 88.63 0.42 1.56 0.61 0.04 0.00 106 0.07 5.44 1.04 2.19 88.630.42 1.56 0.61 0.04 0.00 107 0.06 5.06 1.43 2.19 88.63 0.42 1.56 0.610.04 0.00 108 0.06 4.67 1.82 2.19 88.64 0.42 1.56 0.61 0.04 0.00 109*0.07 5.75 0.65 2.27 88.32 0.42 1.88 0.61 0.04 0.00 110 0.07 5.37 1.042.27 88.32 0.42 1.88 0.61 0.04 0.00 111 0.06 4.98 1.43 2.27 88.32 0.421.88 0.61 0.04 0.00 112 0.06 4.59 1.82 2.27 88.32 0.42 1.88 0.61 0.040.00 113* 0.07 5.37 0.66 2.66 88.31 0.42 1.88 0.61 0.04 0.00 114 0.064.98 1.04 2.66 88.31 0.42 1.88 0.61 0.04 0.00 115 0.06 4.59 1.43 2.6688.32 0.42 1.88 0.61 0.04 0.00 116 0.05 4.21 1.82 2.66 88.32 0.42 1.880.61 0.04 0.00 117 0.05 4.21 1.44 3.05 88.00 0.42 2.19 0.61 0.04 0.00118 0.05 3.82 1.82 3.05 88.01 0.42 2.19 0.61 0.04 0.00 119 0.04 3.442.21 3.05 88.01 0.42 2.19 0.61 0.04 0.00 120 0.05 3.75 1.44 3.52 88.000.42 2.19 0.61 0.04 0.00 121 0.04 3.36 1.83 3.52 88.00 0.42 2.19 0.610.04 0.00 122 0.04 2.97 2.22 3.52 88.00 0.42 2.19 0.61 0.04 0.00 123*0.08 6.45 0.65 1.64 88.56 0.42 1.57 0.60 0.04 0.00 124 0.08 5.99 1.031.72 88.56 0.42 1.57 0.60 0.04 0.00 125 0.07 5.53 1.04 2.19 88.24 0.421.88 0.61 0.04 0.00 126 0.06 4.84 1.42 2.50 88.24 0.42 1.88 0.61 0.040.00 127 0.08 5.98 1.04 1.64 88.71 0.42 1.48 0.61 0.04 0.00 128 0.075.86 1.04 1.81 88.65 0.42 1.49 0.61 0.04 0.00 129* 0.07 5.89 1.04 1.7888.60 0.42 1.55 0.61 0.04 0.00 130* 0.07 5.88 1.04 1.79 88.66 0.42 1.500.61 0.04 0.00 131* 0.08 6.41 0.65 1.65 88.65 0.42 1.49 0.61 0.04 0.00Sample No. x′ y′ z′ n′ 101* 0.07 0.21 0.18 5.19 102 0.12 0.21 0.18 5.19103 0.16 0.21 0.18 5.19 104 0.21 0.21 0.18 5.19 105* 0.07 0.25 0.18 5.18106 0.12 0.25 0.18 5.19 107 0.16 0.25 0.18 5.19 108 0.21 0.25 0.18 5.19109* 0.07 0.26 0.21 5.18 110 0.12 0.26 0.21 5.18 111 0.16 0.26 0.21 5.19112 0.21 0.26 0.21 5.19 113* 0.07 0.30 0.21 5.18 114 0.12 0.30 0.21 5.18115 0.16 0.30 0.21 5.18 116 0.21 0.30 0.21 5.19 117 0.16 0.35 0.25 5.18118 0.21 0.35 0.25 5.18 119 0.25 0.35 0.25 5.19 120 0.16 0.40 0.25 5.18121 0.21 0.40 0.25 5.18 122 0.25 0.40 0.25 5.18 123* 0.07 0.19 0.18 5.14124 0.12 0.19 0.18 5.14 125 0.12 0.25 0.21 5.14 126 0.16 0.28 0.21 5.14127 0.12 0.19 0.17 5.19 128 0.12 0.21 0.17 5.15 129* 0.12 0.20 0.18 5.16130* 0.12 0.20 0.17 5.16 131* 0.07 0.19 0.17 5.15

EFFECT OF THE INVENTION

The present invention provides sintered ferrite magnets having such ahigh intrinsic coercivity Hcj as to prevent it from being demagnetizedby a demagnetization field generated when it is made thin, while keepinga high residual magnetic flux density Br, and further having a highsquareness ratio Hk/Hcj, if necessary.

1. A sintered ferrite magnet consisting essentially of an M phase, whichcomprises as indispensable elements: an A element, which is Sr or Sr andBa: an R element, which is La or La plus at least one of rare earthelements including Y; Ca; Fe and Co, said magnet being produced throughsteps of pulverization, molding and sintering of a calcined oxide magnetmaterial consisting essentially of an M phase and, having a basiccomposition represented by the following general formula (1):A_(1−x−y)Ca_(x)R_(y)Fe_(2n−z)Co_(z)O₁₉ (atomic ratio)  (1), wherein Cais added in the form of a compound in an amount of x before calcining,and said sintered ferrite magnet having a basic composition representedby the following general formula (2):A_(1−x−y+a)Ca_(x+b)R_(y+c)Fe_(2n−z)Co_(z+d)O₁₉ (atomic ratio)  (2), inthe above general formulae (1) and (2), x, y, z and n representing theamounts of Ca, said R element and Co and a molar ratio in said oxidemagnet material, and a, b, c and d representing the amounts of said Aelement, Ca, said R element and Co added to said calcined oxide magnetmaterial in said pulverization, which are numerals meeting the followingconditions: 0.13≦x≦0.25, 0.1≦y≦0.6, 0.6≦[(1−x−y)/(1−y)]≦0.79, 0≦z≦0.4,4≦n≦10, 0≦b≦0.2, 0.13≦x+b≦0.4, 0.1≦y+c≦0.6, 0.1≦z+d≦0.4,0.56≦[(1−x−y+a)/(1−y+a+b)]≦0.72, 1.1≦(y+c)/(z+d)≦1.8, 1.0≦(y+c)/x≦20,and 0.1≦x/(z+d)≦1.2.
 2. The sintered ferrite magnet according to claim1, wherein all of the R element and the Co are added in a mixing stepbefore calcining.
 3. The sintered ferrite magnet according to claim 1,wherein all of the R element and part of the Co are added in a mixingstep before calcining, and the remainder of the Co is added in apulverization step after calcining.
 4. The sintered ferrite magnetaccording to claim 1, wherein all of the R element is added in a mixingstep before calcining, and all of the Co is added in a pulverizationstep after calcining.
 5. The sintered ferrite magnet according claim 1,wherein part of the R element and all of the Co are added in a mixingstep before calcining, and the remainder of the R element is added in apulverization step after calcining.
 6. The sintered ferrite magnetaccording claim 1, wherein part of the R element and the Co are added ina mixing step before calcining, and the remainders of the R element andthe Co are added in a pulverization step after calcining.
 7. Thesintered ferrite magnet according to claim 1, wherein part of the Relement is added in a mixing step before calcining, and the remainder ofthe R element and all of the Co are added in a pulverization step aftercalcining.